Nick,
First: try disabling any power save and sleep feature in the System Settings.
Second: initiate a First Aid scan on the hard drive.
Third: Download any available updates from Apple.
Fourth: While you are in Safe Mode close the lid and open it again and see if the problem replicates.
If the problem does not replicate in Safe Mode it might be good to perform a fresh install after you back up your data.
This will tell you whether you have an issue with hardware or with the software.
I would love to hear the results of the steps above.
Thank you,
Michael