2 1/2 year old sleeping help!!!!

My Ds has been sleeping through the night, no problem since 3 or 4 months old. He is now 2 1/2 and for the past wek, he wakes up crying every 2 hours and either screams in his room or comes and knocks on our bedroom door. I try letting him CIO because that worked for us when he was 3 months, but now he just screams so loud that he wakes up my other 2 kids and then it's just a cry fest. I don't know what to do-he's not sick, he's not teething. Any advice would be greatly appreciated.

Re: 2 1/2 year old sleeping help!!!!

DS did this right before he turned 2. I'm still not sure why, but he seemed terrified to be alone in his room. Since he was scared, we decided not to let him CIO. One of us would sit with him until he fell asleep. With the middle of the night wake-ups, we wound up sleeping on the floor of his room--if we were there with him, he went right back to sleep, and that way, we got to sleep too (though not so comfortably)!

What set this off exactly, I sitll don't know, maybe just his age,, hard to say. He had been a great night sleeper before that.