I took some allergy medicine and now I am literally shaking like I had an adrenaline burst. How the fuck do I calm down?
Flex large muscles, such as quads, glutes, arms, back, all at once. Keep flexing for about 5 seconds, then slowly stop flexing.
Take a warm/hot shower.
Keep warm.
Is the active ingedient dipenhydramine? That's normal, it will wear off in a few hours. Just don't take more, you will start hallucinating horrifying shit.
Use the energy. Run until you can't run anymore, take a breather and run some more until you're burning up. Put on some music and dance. Go for a swim. You can relax later.