My 6 month old started sleeping on his belly at night. he woke up this morning and his eye on the side he was laying on is swollen. is that normal if he laid on that side all night?

It can be..: If your child remained relatively still most of the night it could be dependent edema or swelling from positioning. If the swelling does not resolve after a few hours of sitting up and/or other symptoms develop see your pediatrician or health care provider.

Yes: This can happen however, it should resolve within a few hours of being awake if it doesn't then he should be seen.

Eye swelling: It could be due irritation of the skin from laying on that side all night. If it gets worse it could be an allergic reaction or some other issue. If it gets worse, i would take him to his pediatrician.

Yes: As long as the swelling goes away in a few hours, you shouldn't worry. If the swelling persists, if it is consistently on the same side, or if there is any discoloration of the skin i would recommend you see a pediatrician.