I didn't say sleeping. You'll be lucky to get any sleep. You'll be constantly exposed to every little stray thought or dream a person has, and believe me, you humans aren't quiet or careful with your thoughts. The less control you have, the more the thoughts bombard you.
No, it would be intense, over-loading pain. Nothing but another telepath would be able to snap you out of it if it got that bad. Or it could damage your brain.
I don't like the idea of someone entering my mind anymore than you do, but I've been telepathic for over nine hundred years... I know a little of what I'm talking about. And I promise, it's painless and I don't poke around where I'm not wanted.