I had a eeg done & my doc told me i could be having some type of seizure when i sleep... what can this mean?

A seizure: Is a little bit like a short circuit in the brain and may be related to poor oxygen consumption. If you have symptoms i expect that your doctor prescribed an anti-seizure drug. If no symptoms it might be as simple as poor diet.

Not clear: Some epileptics do have their seizures, which represent uncontrolled electrical firing of nerve cells, at night only, but it helps to have a description from an observer. An abnormal eeg can be nonspecific, such as in migraine or prior head injuries. Do you instead have a sleep disorder? This needs clarification, and confirmation. See a local neurologist.