3 year old weeping for no reason?

He puts face inbetwen his arms and lays down face down, and weeps, and cries, after he's done (usually 2-5 minutes) he either sleeps, goes back to playing in a bad mood, or clings to me and I comfort him, then he goes to sleep.
I dont know why he does this, we love him to death, provide him with everything he needs, he has a little brother, 1 year younger, they play together. We always play with him, teach him, and talk to him. We reward him when he does something right or accomplishes something.
He is an extremely bright and intelligent child.

I just dont understand why he's been doing this.

I've seen him do this three times now.

[littlebit667]

Sound like he is letting stress out by crying.  He may be wound up and releasing by crying.  Maybe you can figure out what is stressing him out and try to stop it before he gets there.  You might find another way to help him destress.  Hitting a pillow as a game,  taking a 5 minute rest with a book.  

[margypops]

Does he get as much attention as his younger brother , sometimes older children are upset when a sibling comes along , they feel left out, one to one time for him helps .Get Dad doing things with him, just him, ball games having fun .You may think he gets plenty of attention but he may not.Does he go to day care or school ?

[tiredbuthappy]

or, conversely, maybe he needs a little space? If he is always being engaged, either by sibling or parent, he may just need some time to himself. I would suggest you work together to make a special place in your home that is just his- somewhere he can go for some private time. It can be a box big enough to crawl in to that you decorate, a pop-up tent you keep up, or a safe place under furniture. My daughter has something she calls her "tiny place" (pillows under an easel). When she needs some space, she goes there. It's OK for kids to feel overwhelmed tired and giving him a place to go tells him it's OK. Afterwards, try to get him to express how he was feeling.