Galaxy A5 2016 sometimes won't wake up, screen flashes

[Tessicorn]

Hi, I have this phone for over 2 years. Today I experienced my phone not being able to wake up when I use the power button/home button. Whenever I push the button, the screen flashes for like 1s blue color, you can also see that the notification panel is blacked out and it doesn't wake up. It takes about 10 tries to wake it up. But it also doesn't happen all the time.
Fortunately my alarm worked perfectly this morning and was able to wake up the screen but right after I slid the bar to stop the alarm, it went back to sleep and was unresponsive for quite some time.
Any ideas what it could be?