C.P.
Just off hand, without really knowing your son, I would say it is just a phase. About 2 years old children become a lot more aware of their surroundings. My daughter was so scared of the eagles in her room. My mom just opened the front door and chased them out. The problem was solved. Later, I figured out that she had seen a picture of the American Eagle and it had piercing eyes. Maybe your son has seen a scary picture and it gives him nightmares. You might make shadow characters with him or play some fun games in the dark. Children usually have a really good memory so even if it happened a few months ago it may be something that he recalls. (It also may be a ploy to get in your bed) Kids are very smart! The only stupid question is the one that you don't ask! Never be afraid to ask. Motherhood is quite an experience, but I love it everyday.