My sympathies for your lack of sleep! I know how crazy it can make you!
It does sound like your son is afraid of something. I agree with the other poster who said to start by talking to him. I have a 2 year old, as well, and although she's a late talker, she can tell me if something is owie, or show me what she's scared of. I find that taking her fear seriously and talking through it with her (explaining the noise outside, taking her to see the tree that's making the shadow, etc) actually does help.
Of course, it could be something harder to figure out with just the two of you, in which case I really wouldn't hesitate to talk to a child psychologist. It doesn't mean anything's wrong with your child, it just means that you need help interpreting someone who can't fully express himself yet. I've had experience with two serious cases of what you describe, and both had concrete causes that required some extra help. First, my little sister was like this just after we moved when we were children. She ended up sleeping on a mat on the floor of my parents' room for a couple of months (not my parents' first choice, but better than not sleeping!) She was having terrible nightmares--we still don't know exactly what they were about (she's an adult now, and remembers little bits of someone trying to steal her)--but she was clearly terrified. The second case was with a little girl I nannied for--she was adopted from Korea through a reputable Christian agency, but as a toddler started having screaming fits when we put her in her big girl bed at bedtime. With help, we were able to determine that she was most likely physically restrained or tied up in the home where she spent the first couple of months of her life, and those experiences as an infant were coming back to her through associations when she was older. Again, we could find strategies to deal with her fears, and really the transformation was pretty remarkable, but we did need some outside help to figure out what the source was.
I hope you can figure out what's troubling your little guy, for everyone's sake! GL!