Frequently my mouse and keyboard (both connected to my iMac) lose connection when iMac is sleeping. So Mac has to be rebooted in order to regain connectivity. Any ideas why?

The following will require any USB keyboard and mouse. If you don’t have them, borrow or buy them, they are inexpensive!

• Connect the USB keyboard and mouse to the computer.
• Open System Preferences – Bluetooth
• Un-pair the wireless keyboard and mouse.
• Turn off Bluetooth
• Restart the computer in Safe Mode per the directions in https://support.apple.com/en-us/HT201262
• Restart the computer normally.
• Open System Preferences – Bluetooth
• Turn on Bluetooth
• Re-Pair the wireless keyboard and mouse.
• Unplug the USB keyboard and mouse and begin testing the wireless devices again.