Getting exhausted all day after orgasm

Everytime I have an orgasm in the morning (doesn't matter if it's from sex or masturbation), I feel super tired all day, with some kind of brain fog. Is this normal ? Does it happen to anyone else ? I'm asking the question because my girlfriend is usually in the mood in the morning and this is becoming an issue for me because if we do have sex, the day is kinda ruined for me after