I had a go in the UK Plantronics anechoic chamber last year on a factory visit. They have a webcam, and an egg timer on the wall. It's not odd for people to weird out if they spend any time in the chamber. The (digital) egg timer was there so you could set it for 30 minutes and it would hopefully snap you out of any spin you got yourself into.
I was in there for no more than five minutes, and it was extremely disorientating. You really can hear the blood in your ears. It's very much like the sound you get from sea shells. I can easily imagine losing my shit in short order in there.