Hi, I am a 24 year old Male I have been

Patient: Hi,I am a 24 year old Male. I have been with my partner for 3 years now. We very rarely have any problems in the bedroom, however I have noticed that when we try intercourse first thing in the morning, like literally upon waking up, I cant seem to retain my erection for very long. I normally can retain it for as long as necessary, and the only times I have struggled with it, like I say have been upon wakening. For example, yesterday we tried upon waking up, and it didnt last very long, however a few hours later we tried again and everything was fine. Is it just because of my bodies tired state upon wakening that causes this to happen from time to time?