One of the thoughts I have when I get exahauted after playing a point and I have to serve is that I tighten up.
I usually just go with the flow and end by solidly my grip and tapping the ground a few times. This works well on the deuce side
On the ad side serving , if I'm equally tired after a long point I don't ever want to grip tight so I end up gripping at the bottom edge of the handle and then set up the rest of my body before I am ready
I'll then start the serve by gripping back up the handle