As people mentioned, selling when things have already tanked is never a good idea. Obviously no one knows how low things will go, but generally when people are panicking about things going much lower, it never happens, or at least to the extent people say. If you're out of the market when a potential v-shape recovery happens or some massive day of upside, that's when you're at risk of missing out of the most gains.
I personally do dynamic dollar cost averaging where I have ranges of prices where I buy the same amount, and if it goes lower, I buy more. And if it dips even lower, I buy even more. I obviously can't do that forever if things just dipped like crazy over a course of a year or 2, and it all depends on how much cash you have on hard or how much you put in from each paycheck, but it's worked really well over the years.