- Platforms
I've done this often since I was little, and normally it doesn't bother me - although it can freak out others sometimes, lol.
The problem is that when I sleep *really* deeply, I sometimes don't move or switch positions during sleep, and I'll lay with my open eye (whichever side) laying on the pillow, drying out until it gets so dry that I wake up with fiery stabbing pain and agony in the bone-dry eye. It's so bad that I struggle to return to sleep for a long time when it happens and then my vision is all blurry in that eye for at least a full day. I can't stand it, but not much I can do about it. It just happened again last night, so it's fresh on my...eye.
tldr
The problem is that when I sleep *really* deeply, I sometimes don't move or switch positions during sleep, and I'll lay with my open eye (whichever side) laying on the pillow, drying out until it gets so dry that I wake up with fiery stabbing pain and agony in the bone-dry eye. It's so bad that I struggle to return to sleep for a long time when it happens and then my vision is all blurry in that eye for at least a full day. I can't stand it, but not much I can do about it. It just happened again last night, so it's fresh on my...eye.

tldr
