Due to health issues, I couldn't make it in neet this year. Is it too late now to take a drop?

Hello
If you have confidence in you then it's still not late to start for the preparation. As you said you had good preparation then there won't be a problem in recalling things . You just need to start it as fast as you can so that you can complete everything on time.  Scoring 393 in first try isn't bad just work hard in determination you would surely succeed.
Goodluck