What the hell is this that's just appeared?

[FrazzleRock]

What the fuck is this? It's literally just appeared as we're watching a film. I felt my arm with my left hand and was like "what the hell is that?" Looked down and saw this. Not whacked it or anything. Not sore, but there's a lump which you can see in second pic. It's the inside of my upper right arm
It deffo was not there minutes before

Remains a mystery then. It's still there

Don't know, sorry! But bumping for you in case you don't have an answer in rl.

The bruise? I get marks like that on my fingers if I burst a blood vessel. It happens if I open bottles sometimes. Grip a door handle too hard. Could you have pinched and twisted your inner arm somehow? Attempting to crack walnuts with your muscles is the only thing I can think of though...

Thanks for your responses. I've not knocked or pinched it. So odd.
DPs nurse friend suggested anemia which is actually quite likely as I'm usually borderline and I have been exhausted large past few weeks. Plus I saw several pale small bruises on my legs where I may have knocked and not realised. Though I'm not sure what the lump underneath the bruise is. Seems like a burst blood vessel or something but I can't understand why. I've not had any blood taken recently.
I'm going to call NHS Direct tomorrow and see what they can come up with

Good that you're going get medical advice. Hopefully just anemic but you ought to get checked out in case you've developed ITP (problem with your platelets, serious if untreated but very treatable).

Thanks Bat. I called NHS Direct last night. She asked me loads of questions and said I was right to call them. She wasn't terribly concerned as I'm not in pain and it appears to be healing - It is going yellowy around the edges now.

She said I should contact GP within three days and contact NHS direct again is things get worse. I have a GP appointment for Tuesday morning. I'll mention ITP if she doesn't bring it up.

The anemia thing does still make sense to me, but I don't understand why there would be a lump underneath the bruise. Hopefully all ill be revealed soon....

I had something like this appear on my hip last year. I don't know where it came from and it never happened again!

I think it looks like an insect bite. Can you see any tiny pinprick marks at the centre of the bruise? Would explain the suddenness - I once got bitten by something (in the UK, so not any exotic tropical insect or anything!) and the bruise appeared very quickly and covered half my arm. Could it be that?

I had something similar appear for no reason in my wrist (think the bit where the watch strap buckle goes). It freaked me out but there was no pain and it just disappeared of its own accord in about a week.