iMac won't wake up from sleep

Apple Support said to try this. I did, but I won't know if it worked till it fails again.

If your Mac doesn't sleep or wake when expected

How to reset NVRAM on your Mac

Reset the System Management Controller (SMC) on your Mac

I have this issue now on my iMac 27". Started after I updated to High Sierra. I have to reboot. I can hear the fan running but my bluetooth apple keyboard and apple track pad do not wake the computer up. I have to hold the power button until the systems shuts down then start up again.

Same here, fresh install of High Sierra. I have a Mac Pro 2013 Tube, 4 times in 24 hours when I came back to my computer after an hour of not using it... the system will not wake up. My screens seem to start the wake up process, but remain black, but they are on. I have a sound program that is active on the system, BitWig, with software synthesizers and I can play the sounds but the screens are black. So the system is not locked up, I'm just not getting video to the monitors.
Very frustrating. This is horrible. Regrets
Next time I will attempt to put in my log in code and see if that works. I forgot tot try that before I rebooted.
Andy

I upgraded this morning and have had to restart my computer 3 times today after going to sleep???

Hey ronymrad,
I understand that you are having issues with your iMac not waking from sleep. Let's see if we can get this sorted out.
I would start with making sure that your iMac is not in safe sleep. Press the power button on the back to see if it wakes up then. If that does not work, take a look at the information below for more details on how to troubleshooting this further.
If your Mac doesn‘t sleep or wake when expected
https://support.apple.com/en-us/HT204760

If your Mac doesn't wake when you expect

Your Mac might pause a few seconds before it wakes up. If it doesn't seem to wake at all, check for these possibilities:

• Your screen brightness might be turned down.
• If you're using an external display, your display might be turned off.
• Your Mac might be in safe sleep. To wake from safe sleep, press the power button.
• Check for a sleep indicator light, if applicable, and make sure that your Mac isn't turned off.

If the previous steps don't work

These additional steps may help identify or resolve the issue:

• Reset the SMC.
• Reset NVRAM.
• Disconnect external devices other than your Apple keyboard, mouse, and display. If that resolves the issue, gradually reconnect your devices, testing each time, until you find the device that is interfering with sleep. Then check the documentation that came with the device, or contact the device manufacturer.
• Start up in Safe Mode to see if the issue is related to non-Apple startup items, login items, or kernel extensions.
• Try to isolate the issue by using another user account.

Take it easy

Hi ronymrad,
Have you tried testing your sleep issue in a new user as it might not be waking up because of some user setting. Take a look at the next article for the details on that.
How to test an issue in another user account on your Mac
https://support.apple.com/en-us/HT204443
Have a good day

Hello ronymrad,
At that point, if it is still not waking from sleep, something further is going on. I would probably move on to reinstalling OS X. I would make sure that you have a safe copy of your data first. After you have reinstalled OS X and it is still giving you issues, you will want to contact Apple Support for further assistance as it could be hardware. The links below will help you out from here.
How to reinstall OS X on your Mac
https://support.apple.com/en-us/HT204904
Contact Apple Support
https://www.apple.com/support/contact/
Take care