Go to bed first. After an hour or so, your friend should also go to bed, but in a place he or she can keep an eye on you and hear you. You may want to put bells on the doors to the bedroom and bathroom, so you make noise if you get up.
What did you learn? Do you snore? Do you talk in your sleep? Do you thrash around? Do you get up in the night? How often? Even if you experience only some of these symptoms and you're fatigued during the day, call your doctor and ask for a professional sleep study.