just an update to let you know my little one is finally back to sleeping on his own. I had him practice sitting down from standing position in the crib during the day. Once the novelty of standing up wore off he stopped doing it especially when he knew he would have to stand for a long time while crying. He would eventually sit back down & go to sleep by himself. I also started to be much more consistent with his bedtime routine which seemed to really help get him in the right mood. Thx to everyone for your suggestions!