When did this happen? Recently or has it been months? If it's recent, then you could be penalised.
When you get penalised, majority of the keywords you're ranking for will just 'disappear'. Then in a few days, all disappears. It also takes time for all Google's datacenters to update. So if you lose in one country's, you may lose the rest in other countries later as their datacenters sync. It also takes a couple of days for any 'penalty' to show up in your GSC.
There's also a suspected ongoing Google update. However, If you're hit by an algorithm update, it shouldn't be this bad. You should still have about 20-30% of your total keywords still ranking even if you got hit, though lower positions.
I would advise you to wait for a few days. Perhaps by Monday then you should know the answer.
By the way, if you do site:yoursite. com in Google, does it still show? Any drop in search results for your website? And did you engage in any shady backlinking services or do anything recently to your website?
And what niche are you in? If your niche is relating to music or movies downloads, then you may have gotten DMCA takedowns in Google which resulted in your rankings for certain search keywords to disappear.
Also, if your keyword rankings have already disappeared for a few months, then it's very likely Google is either omitting your website from the search results (can happen if there are too many duplicates), or simply refuse to rank it due to it being poor quality (especially if you plagiarise a lot, or the content literally offers little to no value to readers).
As you can see, there are many factors that needs to be considered before we can give you a definite answer. But for now,