Cubital tunnel syndrome can cause an aching pain on the inside of your elbow. Most symptoms, however, occur in the hand. Numbness and tingling in the ring and little fingers are common symptoms of ulnar nerve entrapment. These symptoms may come and go.
Are you sitting in front of a computer a lot? At a guess, it might be not moving your elbow much + pressure to it when it rests on a table causing your nerves to be squeezed too much.
Edit: probably the same thing Archdemon wrote above.
It's just my random guess, though I had something similar happen a few times after writing or playing games for a long time without pause; in my case it all passed after a minute or two though.