I know, i always feel like that comes next, but worrying about that can sometimes force you into a depression you may not have been in.
I was hypomanic a few weeks ago then suddenly started getting so panicky about being depressed that i upset myself, and caused it.
You cant do much to stop an episode, but you can try your best to not actually bring it on, well thats easier said than done.
Find something to focus on. my minds been racing everywhere at the moment, so i've been watching youtube videos i wouldn't really watch, i'm watching people who speak quite manically and keep my attention. Its a good technique for me, something new, that doesnt involve anything harmful but keeps me focussed.