What caused this? & how to do i solve it?.

I'm pretty sure your CPU (Central Processing Unit , your processor) was overheated (the fan thingy , intel usually). If it was your GPU (Graphics Processing Unit , your GFX Card) your fps would've dropped like mine does sometimes.
And i'm saying it's your processor because If you use a Speedhack and set it to negative (-5 Speed for example , instead of +5 for 5 times faster) This is what happens. The slow effect with the teleporting people.. your game refreshes every like 3 seconds and the "slowed people" appear in their right locations if they move.

 

If you have any of the Intel/AMD multi core chips its probably the internal thermal control kicking in , when a core or miltiple cores get over a certain temp it will under clock itself to try and prevent dmg/crashing. Usually you dont notice the effects but if its drastic enough it does massively slow down the PC (although im really unsure as to why u get slow motion lol id expect just horrid lag). You can turn this feature of in bios usually but if you do i suggest you set your overal tempreture warning to a lower temp and make sure it doesnt over heat