Fps drops after a while

I am building an Unity application as a visual stimulation for a neuroscience study. Basically, my application just shows several flickering planes periodically. However, I noticed that every time after I ran the application for a few minutes, the fps dropped to around 10~30 shown in the profiler. The drop of fps happened in both editor mode or build. Since my script is totally in cycle, I am guessing there were some accumulative issues like GC or memory leak?

Also, I noticed that when the fps starts to become unstable, I can click the Pause button in the tool bar of the Editor and then resume the application, the fps will become stable for a further period. Therefore, I am wondering what actually happens when the Pause button is clicked? Does pressing the Pause button clear or reset anything so the fps can go back to full?

@q89123003
Any screenshots?

Okay. Are you using lots of particles, and lots of fancy post processing effects, in your project? If you are, that could probably be some of the reasons, why the slowdown occurs.