Why does my second monitor flash on and off?

Why does my second monitor flash on and off?

Starting yesterday and getting intermittently worse the longer I use it, occasionally my second monitor will turn off, it will read ‘no signal,’ then flash back on. This is getting quite frustrating as it resets all my opened screens to being on one screen. Please tell me how to fix or what the issue is so I can replace whatever isn’t working. Thanks!