Mistress has me wear a butt plug overnight about 5-6 times in a given month or so. I've always felt that the most difficult aspect of it was finally falling asleep while being so aroused. The first few nights will not be very restful. After some experience, and some investments in thicker and longer-lasting lubricant, I have found myself honestly enjoying spending the night plugged. I especially love forgetting that it's in there and being reminded of the plug's presence as soon as I move around... definitely becoming a favorite way to start my day ;D
I must add that overnight plug wear should generally be left to medium-sized plugs only (unless you're wanting a really sore bottom the following day...). Small sized plugs will more than likely slip out at some point during the night.
Anyone interested might find the following advice on the topic written by Tristan Taormino to be quite helpful: link