If it is intermittant I would think it would be more likely to be mixed than akathesia, just based on my rounds of akathesia. One of the worst parts of akathesia for me has been that it never lets up. Not when I need to sleep, not when I need to eat (so I have trouble eating because it is impossible to sit still), not when I need to drive and not fidget horribly, etc. Maybe it can be different but that's my experience. Mixed episodes can sometimes feel like they improve and get worse for me when really I am just getting a bit more hypomanic for a while and then bouncing back to dysphoria. I don't often feel improvement while mixed that is brief but it has happened for brief periods before.