I went through a period a few years ago where I had dozens of bruises on my body all the time - some of them were pretty big too. Some I remembered getting, others I suspected were happening when I was asleep (I can get up and go to the toilet without waking up, but would occasionally walk into stuff), others I really have no idea. I went to the GP and had blood tests every fortnight for about 4 months, as he was a bit concerned that I looked like someone was injuring me - I had one that was clearly a handprint, from someone just touching me. It stopped after about 9 months; I still don't know what it was as the blood tests all came back normal. I still bruise quite easily, but not from normal contact with people.