I would guess that you have caused these bruises while you were sleeping as well, but if you say that you don't remember anything about it you might need to search for an answer somewhere else. Could it be that you had some activity on the day before this happened that could have caused the bruises? Bruises usually take some hours to show up and you might need some time to notice them. Other then that there are also illnesses that can cause such symptoms, perhabs a clotting disorder or something like that. These would be my theories if there was no external cause. Of course I ain't a proper doctor or something and if it was indeed some clotting disorder it could have severe consequences if you don't treat it properly.
i say go to the hospital the bruising might be becuase you were tossing and turning at night and you are low on platlets just go in for a blood test and ask for a CBC
Sleep walking and bumping into furniture? Maybe something paranormal? I once woke up with bruises around my ankles which looked much like ligature marks. What's up with that???