Macbook Pro overheating issue? I don't know why, but these days my fans for some reason run throughout the day. When the fans start spinning the computer becomes extremely laggy. I have also tried running Macs Fan Control app after reading about it, but my system still hits 80°C. At that time it also freezes for 5 seconds to 2 minutes. 

So any suggestions as to why it might be happening, and how I can fix it?

System:
Running macOS High Sierra 10.13.3
MacBook Pro (15-inch, Mid 2012)
Processor: 2.3 GHz Intel Core i7
So any suggestions as to why it might be happening? Is it overheating?


No, it's not overheating.  It's actually attempting to prevent an overheat condition.

Your MacBook Pro is doing two things to keep the CPU/GPU within operating temperature tolerances:


spinning up the fans, to cool the CPU
allocating CPU to lower the load demand


When you install software to override the SMC's control of the fans (cooling), you force the system to increase the CPU allocation to prevent additional load - it will become slower.

What you should do is 


clean the dust from the fans
put in new, high quality thermal paste on the CPU heat sink


There are excellent videos on how to do this procedure on YouTube