Ok, I am standing...now what do I do?

So I don't have a picture for this because I would have had to take one in the dark, but I will try to get a picture later. I put Jack to bed tonight but heard noises coming from his room pretty soon after I left. He sounded a little upset and so I opened the door and peeked in. Jack was standing up in his crib, which is a first for him. He was holding on to the side for dear life and his legs looked like he was doing the hula. He was so determined to stand that he didn't think about what would happen once he got up there. Rather than fall onto his backside he just held on and whimpered until I came in. So I laid him down, but a few minutes later I heard the same whimper and caught him standing again! Good thing we already lowered his mattress. Life is going to get a lot more hectic with him crawling and standing!