I was in SP, trying to take a lucid nap, and got to HI/HH, when it sounded like somebody yelled in my ear really loudly. I shot awake and couldn't get back down to where I was.

Is there a way to know when I'll start hearing things so I don't get shocked awake again? Is there some sensation I should be looking for?

I don't have ear plugs, so I can't hear the switch from external to internal hearing. Should I get some? Would that help?