I've seen some outlandish claims about floatation tanks by people that have never done it before. Hallucinations? Hallucinations after the float? Never. Dream visions like the ones gained from meditation or relaxation or WILD, yes.
It ain't drugs. It's like meditation. Advanced bathing. With the lights off. Nothing to be scared of. You can't be scared of a really good waterbed. The tank I float in has lights and underwater speakers you turn on and off yourself.
There is something weird about it, aliens and mad scientists or something. The movie Altered States doesn't help. I assure you, it's a perfectly benign thing to try. It's a great creative tool for me.