As already said, you can take these in bed and fall asleep straight after, this is what I do also.
I put a small towel down on the sheet and then pull it away from under me once my PJ's are back on, I probably don't even need a towel as there is never any mess.
As for interruption, I'm surprised how little I feel the enema at night, it just gets in there and goes on its merry way. I think perhaps it's less of a struggle to keep it in whilst laying horizontally than it might be trying to keep it in whilst upright? I tend to wake up at the same time every morning to pass whatever needs to come out, aside from this chesty cold now keeping me awake, my sleep has been pretty much uninterrupted by the enema.
I actually slept better and got a full night sleep the night I first administered it - no multiple trips to the toilet with diarrhea!! Best night ever.
It's worth a try for a couple of nights just to see how you get on :) Good luck