@lotsofpain
That is quite a unique I.D.
First I have these type wounds all the time. You did not give your age. What I was told when you get older (I am 78 next month) your skin looses collagen. This makes hitting your skin causing damage and will get a lot of bruises and bleeding.

If you don't remember bumping your skin or arm that could indicate something else. What I found when I was younger a minor bump would not cause a bruise. But now I can just bump something and bam a bruise. I do take aspirin but dermatologist found I have lost a lot of collagen.

Now no medical advice from me. We on MCC are here to share or persoal expereinces. The information I passed on was came from my Mayo PCP and my Mayo dermatologist. So my response is specific to me, specific to my skin, and what has been causeing my bruises.

You need to show these type injuries to your doctor. They can determine if nothing to worry about and then you have that information next time it happens or they may want to look into further as you said you do not remember bumping into something.

Example: I once had a bruise after a I.V. was taken out. I thought nothing of it because I was getting so many bruises and was told not to worry about them. But the bruise was spreading and more and more pain the arm.
I took a picture of my arm and sent it to my cardiologsit via Mayo portal. They brought me in and did an echo. Turned out the I.V. spot developed a blood clot and my vein going up my arm was blocked.

Are you on blood thinners? They will really add to bruises and bleeding from minor bumps and injuried. Just to be safe show these type things to your doctors (I take a picture and send to Mayo via portal) who can rule out something and ease your mind in future or they may need to check especially if these is something new and you had no memory of bumping or injuring the location.