The Cortisol explanation makes sense. Also, using a mantra. For me, I think I read somewhere that upon waking, your blood sugar is low and that can add to some anxiety. So, on mornings when I feel that "jittery" feeling, I keep telling myself "it's just your body's FEELING, it's not your mind", which helps keep that "anxiety circle" from starting. Then I strenuously focus on saying exactly what I'm doing every moment ( I'm just sitting on the toilet; I'm just waking down these stairs; I'm simply letting the cat out; etc) [that may be part of CBT, I don't know]. And finally, I remember to drink a glass of juice (no added sugar) before eating anything else to help immediately bring up my blood sugar. Well, I also usually take it with an L-Theanine capsule. On about
6 recent occasions I've needed to get past those morning "uh oh" feelings, this routine has always helped me.
Best of luck, and keep coming back here. These folks have great advice/support! :)