This reminds me of when I was considering changing from just sport diving to becoming a salvage diver. I was talking to one of my friends who does it for a living and he had one of the old MK V deep diving suits in his collection of old diving gear. I'm not normally claustrophobic, but when I tried it on, the moment they tightened the helmet down to the suit it was almost panic inducing. I've had incidents at depth before with my scuba rig, but the very idea of being that isolated and having to rely on air being pumped in from the surface while you're a couple hundred feet or more down was a terrifying thought. It's no where near as complicated as a space suit, but I imagine the experience is similar, knowing if something goes wrong it's going to take you a few minutes minimum to get back to an airlock and safety and having the visor inches from your face all the time.