First off, make sure you are in the proper physical condition for diving. It can be rather demanding considering how equipment intensive it is.
Next, make sure you're properly hydrated. That can contribute to feeling of fatigue as well.
I'm going on the assumption that you are a fairly new diver. If this is the case, you might also pay attention to your breathing pattern. If you still have that slight edge of anxiety that some new divers feel, you might have a bit of CO2 retention going on which can also contribute to feeling tired or hungover. Try making a concious effort to exhale slowly, fully, deeply several times in a row throughout your dive.
Last, make sure you're staying well within your NDL limits and that you are taking your time and coming up slowly, especially after your safety stop. A couple of short stops (a minute) at half of your deepest depth might benefit you also.
As a side note, does your buddy show any of the same symptoms while diving these profiles with you? Do you get your tank fills at the same place for all of your dives, or does this occur at multiple locations with multiple tanks?
BTW, I am not a doctor, nor do I play one on the internet. All of the above is general recommendations, not medical advice. If you continue to experience problems, you might consider calling DAN for further advice.