For me, anxiety is the big one — the real pressing problem for the largest number of people, that can be most helped by floating. By far the best review of the subject I know of is the video below by Justin Feinstein of CalTech. You can just watch it if you like (it’s half an hour and quite accessible), or continue with my discussion below.
“Floating provides a window into the lowest reaches of our brain: a window that allows us to see the rhythm of our life, a window that allows us to literally feel the flow of sentience completely untethered from the external world. … [Anxiety is] a rhythm that constantly outpaces the beat of life itself, and importantly it’s a rhythm that can be slowed down by floating.”