The percocet might be the culprit on making you groggy. I can't take it. Even a quarter tab gives me hallucinations, and makes me groggy for a couple days. I was taking Gabapentin 400 mg 2x a day for about a month before I had to get off it due to being pregnant. I'm back on it 3x a day 400 mg and haven't had any side effects. The first time around it made me feel a bit buzzed (like I'd drunk a little too much alcohol) for about a week then was fine. It also made me want my husband's undivided attention lol. I think that's how we ended up with our youngest son lol. I was also taking lortab 5/325mg for break through pain. Remember we all react differently to meds.