I've noticed in my lucid dreams, after I'm in it for a while my eyes start shutting. You know when you are super tired and your eyes just start shutting and you doze off? that happens in the LD to me and usually ends the dream. Like my eyes roll back.
Example. A few nights ago I had an extremely long LD. It seemed like 30 minutes or more, then about halfway through I started not being able to open my eyes, luckily I caught myself and said some voice commands and the dream continued.
Does this happen to anyone else? how can I prevent it?