Are you doing a lot of brushing and/or a lot of spot healing?
No hardly any. The problem occurs right from start up not slowly over time. Like I said the program was working fine one day and then crapping out the next.
What is your version NUMBER of Lightroom. (I want the number, not words like "up-to-date")
Try turning off the GPU acceleration (go to Preferences, click on Performance, uncheck "Use Graphics Processor")
This sounds a lot like a bug that was present in an older version of LR so indeed we need to know the version number of Lightroom and the operating system. The current version is CC 2015.12. Is this a retina MBP? If so, it's usually best to keep the GPU acceleration on as they have high enough resolution screens where the GPU acceleration does help but toggling it on and off to see whether LR's behavior changes is a good idea.
Lastly, make sure to check for any hardware issues on your MBP. Even for the version that showed the fatal slowdown, that was usually only after some use. Run a Repair on your hard disk from Disk Utility. Are you running any antivirus software?