Quoting sambugjoebear:" I wouldn't think it's because of the baby. He's been nothing but excited ever since he's found out that ... [snip!] ... 3 more hours until you can be up." That's when he starts saying that he's scared and makes a lame excuse as to why he's scared."
It sounds like you need to just sit down and talk with him about getting up in the middle of the night. It's kind of a delicate matter, as you don't want him to feel like he can't come to you, but you also don't want him waking you up simply because he doesn't want to go back to bed. My oldest went through this for a little bit when he was around 4 or 5, I ended up sleeping on the couch for about a week so that I could catch him as soon as he got up and send him back to bed before he could fully awaken. Your son may be having a hard time returning to sleep because of the over head light, so if you can, try to turn it off or use a less bright light after he goes to sleep. For a while, i did have to wait until my son was actually asleep before I'd turn the light off, now that he's 9, he's starting to request a pitch black room just like his father, lol. granted he doesn't get to since his little brother is in the same room and refuses to go to bed without a light. It sucks living in a one bedroom house, I wish I could give them their own rooms sometimes, it would make things so much more peaceful, and I wouldn't have to convert my second living room into a bedroom like i do now.