It really depends on how big the meal is. You eat to get energy. If you eat a large meal and sleep your body will retain too much because you are not expending any energy. Though if it's a smaller meal then your metabolism should do well to get only what it needs.
Sleeping right after a meal will cause you to gain weight because your body doesn't have a chance to burn off any calories. This technique has been used by Sumo Wrestlers for centuries. (Have you ever sen a skinny Sumo?)
When u eat, blood goes to your stomach; since a lot of it leaves your brain, u feel sleepy. Go to sleep if u want because the calories are the same whenever u eat. You can burn them off the next day or whenever u want.