I would run the onboard diagnostics to see if something is not working correctly. Your system will go into CPU Safe mode which reduces the systems CPU clocking to a crawl!
To get to diags restart your system and press the ***D*** key on your keyboard at startup. Here’s a good reference [https://support.apple.com/en-us/HT201255|Mac startup key combinations]
Let us know what you got for an error/s