I lean on my arm a lot at my computer, and it became half numb. i stopped leaning on it, but it's still been half numb for days. what's wrong with it?

Cubital tunnel: You leaned on your ulnar nerve at elbow, and now have persistent inflammation at elbow, where it may well be pinched due to swelling. May improve over next few weeks, but may need to have injected or treated surgically, but too early to become worried as may reverse nicely. Talk to your doctor soon and devise some ways or protecting the elbow.

Funny bone...: You have irritated one of your peripheral nerves enough that it is not getting better as quickly as it once did. I suspect this was your "funny bone" nerve at the elbow. It will get better with time, and may get better faster with a few days of non steroidal anti inflammatory drugs. You will need to stay off your arm to prevent this from recurring.

Nerve Contusion: Likely you put bruising pressure on the ulnar nerve (at the "funny bone") at the elbow. Your hand pinky side is probably numb and tingling. With avoidance normal sensation will likely return, but not guaranteed. You really need to see a neurologist; not urgently but sooner than later.