Framerate drops during gameplay

Just curious about why I get regular lag. I am on a laptop so it could just be thermal throttling but I am curious if the graphs I have attached could confirm that. The lag happens when the GPU and CPU graphs have a high value.

This performance was always like this. My settings are basically low to lowest everywhere and I have a 30 FPS frame limiter to try and keep the load down so that the temps stay relatively low but I don't know if that does much. If I disable the frame limiter I can get roughly 60FPS initially but it generally does not last long and starts to fluctuate too much to be playable.

I have set the high performance power consumption, I am plugged into mains power and I have all the latest drivers.

Weird thing is that otherwise the performance is acceptable. Any other reason for this behavior other than simple thermal throttling?