I woke up to my phone screen being green.

Hi,

Just verifying that it is a green hue and not an amber colour?

Check if the night light feature has been activated go to Settings > Display > Night Light

Try wiping the cache partition and check, in case it is corrupted cache data that is affecting the screen somehow.

If still no good try starting the phone in safe mode and check.

If it works OK in safe mode then a downloaded app is the cause of the problem. The tricky part is to find out which one is the culprit. You will need to uninstall each downloaded app, one by one and test the phone in normal mode between each uninstall to see if it works OK. When it does then the last downloaded app that was uninstalled was the cause of the problem. A downloaded app is one that you downloaded and installed in the phone and was not pre-installed on the phone when you first got it.

If applicable in your device try mirroring the phone’s screen to a TV and check what its display is like. If it is OK then most likely there is a problem with the phone’s display assembly.

Was the phone on you when you took your nap, just in case you may have inadvertently leant on it whilst asleep?

As a DIY repair you may have to open the phone and first check if the display flex cable connection on the motherboard is OK and if so then to replace the display assembly. If doing this yourself seems too daunting, contact a reputable, professional mobile phone repair service and ask for a quote.