I had a large very dark bruise on upper left arm about 4x2 inches. I do not know how I got it. It took about 4 weeks to start going away (just this past Monday). There did seem to be a small lump underneath it that was tender to the touch. I woke up this morning with a similar bruise in same exact spot. No memory of hitting it on anything. I am 60 year old healthy women on thryoid meds for low thyroid. I take 2 naproxen a day for arthitis in my right hand. Eat well. It concerns me that this bruise has come back before it really was totally cleared up.