My FPS has droped only in CS GO

https://www.reddit.com/r/GlobalOffensive/search?q=fps+fix&restrict_sr=on&sort=relevance&t=all

Revert drivers? NVidia tends to focus only on the newest line, which can destroy the performance of random games on older chips as they release newer drivers.

A recent update probably broke it. It happens to me sometimes with TF2, so I guess it's a Source games thing.
Probably.

Probably because of a new update of the game or drivers. But if you have a 60hz monitor it doesn't matter. Didn't accidentally enable V-sync?

I noticed something weird with my new 1070 too, first time I start the game it lags big time, after a restart it runs smoothly. Since you are also using Nvidia, it could be the drivers being buggy indeed. Try and see if restarting the game (basically starting it for the second time after PC restart) will make a difference.

Sometimes (maybe even allways) CS:GO after update reset settings to default.