Almost a decade ago I made a similar amount in an IPO event being an early employee.

Company of said IPO dropped fairly hard in less than a year (you may be able to guess which one). I'm still not poor by any means but seeing $5~6M turn into $1~1.5M doesn't feel great. Especially since, $5M is retirement money, and $1M is not, so I was literally looking at myself going from being able to retire to not being able to retire.

My advice would be that if this asset of yours could be volatile at all by any means (e.g. is a stock of your employer or even your own company), liquidate and diversify as much as possible as soon as possible.

Then do everything else that everyone else on this thread said about investing, insurance, etc.

(using throwaway because my main account is somewhat recognizable)