The main goal of the present study was to do an initial evaluation of flotation-REST as a treatment of GAD. The sample used was screened with self-report measures extensively used to detect GAD in both clinical and non-clinical populations [29, 30]. The main findings were that flotation-REST significantly reduced both the general GAD-symptomatology, as well as several symptoms associated with the disorder, such as difficulties in emotional regulation, sleep difficulties and depression, while having ambiguous or non-existent effect on level of pathological worry and mindfulness. In addition, all improved outcome variables at post-treatment, except for depression, were maintained at 6-month follow-up assessments.
Considering that GAD has been considered a treatment resistant disorder [16, 52] it is interesting that flotation-REST significantly improved GAD-symptomatology (η p 2 = .062), in which 37 % in the treatment group reached full remission at post-treatment (waiting list control: 14 %). Results also showed that some factors known to play an important part in maintaining GAD (pathological worry and low mindfulness) were not affected by the treatment. A possible interpretation of these results might be that treatment mainly affects physiological factors in the GAD-symptomatology, such as restlessness, fatigue and muscle tensions, thus explaining the reduction of the general GAD-symptomatology, while the core characteristic of GAD, the pathological worry, is left marginally affected. This interpretation is also supported by earlier research on flotation-REST which has shown that the most robust effects from flotation-REST are relaxation  and reduction of muscle tension pains [(e. g.) ]. Taken together this implies that additional treatment is needed to reach full remission of GAD-symptomatology by floating.
However, there was a convincing beneficial effect of flotation treatment on difficulties in emotional regulation (η p 2 = .16), indicating that the awareness of emotions increased, and that the treatment enabled individuals with GAD to better understand and regulate their emotional responses. This is an important finding considering earlier laboratory studies, reporting that individuals who met the criteria for GAD by self-reports measures had higher levels of intensity of emotional experience than control individuals, and in addition exhibited marked difficulties in their capacity to identify, describe, and accept emotional experience . Emotion regulation training has been proposed to be a potentially valuable addition to existing treatment protocols for GAD , in the light of this, flotation-REST might be an asset in the treatment of GAD, targeting this aspect of difficulties associated with the disorder.
The results also indicated that the flotation treatment had a strong beneficial effect (η p 2 = .16) on sleep difficulties, in which 43 % of the participants in the treatment condition were “good sleepers” at post-treatment (waiting list control: 27 %). Co-existence of sleep difficulties and anxiety has been extensively reported in previous studies [(e. g.) ], and approximately half of individuals diagnosed with GAD report having difficulties with sleeping . This underlines the importance of this finding, and suggests that individuals with GAD might benefit from flotation-REST treatment by improving their sleep.
The improvement of sleep could also have contributed to other beneficial effects, such as the lowering of depression, which was the strongest effect from treatment (η p 2 = .34), and where 42 % of the participants in the treatment group reached full remission at post-treatment (waiting list control: 9 %), especially when considering earlier studies which have suggested that sleep difficulties could trigger depression and other forms of psychiatric diseases (e. g. ). The reduction of depression is also in line with earlier research on flotation-REST which has repeatedly demonstrated this effect for various populations suffering from stress related disorders [(e. g.) [20, 21]]. The observed improvements of depression at post-treatment were not maintained at 6-months follow-up, which might indicate that additional booster session is necessary to make this effect of treatment persist over time.
Regarding treatments effect on mindfulness, the groups did not significantly differ at post-treatment, despite that results indicated a considerable significant Time x Group interaction (η p 2 = .17). The treatment group significantly increased their level of mindfulness when comparing baseline to post-treatment scoring, but since the groups differed significantly on this variable at baseline it is hard to draw any firm conclusion about the treatments effectiveness on this dimension.
The several positive effects of treatment observed in the present study suggest that individuals with GAD, in line with what has been confirmed in other flotation-REST studies on various patient-groups [(e. g.) [19, 23, 24]], experienced the treatment as beneficial. Possible the deep relaxation that is induced during the flotation sessions could be a contributing factor to these positive effects from treatment. This is supported by the scoring on the EDN-scale, which has been used extensively in earlier flotation-REST studies [(e. g.) [19, 20]] as an indirect measure of experienced relaxation during the flotation sessions. The significant increase over time for the treatment group on this variable, indicated a normal treatment response of flotation-REST [(e. g.) ].
This study is not without limitations. Even though the sample was identified with self-report measures that has been extensively used to identify GAD in both clinical and non-clinical populations, more research with clinical populations is needed to confirm that the findings is generalizable to GAD patients. The cut-off score used for the PSWQ could also be regarded as relatively low compared to some studies [(e. g.) ], which further underlines the importance to conduct studies with clinical populations to be able to draw any firm conclusions regarding the effectiveness of flotation-REST as a treatment of GAD. There was also a small but significant difference when comparing the groups scoring of mindfulness at baseline, although the level is to be considered low for both groups when considering normative data . This group difference is still somewhat problematic, especially since mindfulness is associated with depression and pathological worry [(e. g.) ]. On the other hand, the scoring on the other assessments at baseline showed substantial psychological suffering for both groups, including the dimensions of pathological worry and depression, indicating that the difference on the mindfulness dimension at baseline did not have a significant impact on the other dependent variables. Furthermore, a sizeable proportion of the the participants received uncontrolled medication and/or psychotherapy. In addition, the CBT interventions received could possible differ in quality, both in regard of the competence of the therapist, and in regard of potential differences in what CBT techniques that were emphasized during these treatments. Although it can not be ruled out that the groups differed in regard to how other forms of received treatment impacted the dependent variables, the effects from these confounding variables should have been addressed by the applied randomization to the sample. That randomization worked out efficiently is also indicated by the chi-square test at baseline and post-treatment, which showed that the groups did not significantly differ in regard to received psychotherapeutic and psychopharmacological treatments. In addition, although no statistical difference was found in regard to received psychopharmacological treatment, the use of medications was somewhat higher for the control group at baseline.
Despite these limitations, the present study provides some initial data which could guide further research in the field. Considering these results, as well as that no negative side effects has been associated with the method either in present or other studies, further research should try to establish that the current findings is applicable to patients with GAD, by conducting randomized clinical trials with active control condition, and by further enhance the study design by for an example blinding the study personnel. It could also be of interest to study flotation-REST combined with a psychotherapeutic intervention, which in earlier pilot-studies [(e. g.) [27, 28] has been reported to be a combination which makes the treatment process more effective. Furthermore, flotation-REST should be explored as a complementary intervention of other types of mood and anxiety disorders, especially those in which emotional regulation difficulties, sleep difficulties and depression are central issues.