What have you done, OP? Did you turn off or turn down all graphics as much as possible? "Particle effect" is one thing I'm thinking of, but unfortunately I built my own supercomputer and thus I run everything at maximum so I'm not really well-versed on how to "turn things down" (or off).
Here's another "off topic" base story, but it's not a bad pun... I am currently playing Monster pack, and every time I fly somewhere and then fly back to my base (I use the MPS powersuit), Minecraft will freeze for a short bit. It will just "hang", the sounds are running but the graphics comes to a complete halt for about 5 seconds. Then, it clears up, and I can move again.
This happens EVERY time I leave the area of my base, and then return to the area. When I return, the whole game freezes for 5 seconds (can't even move my mouse cursor) then it is fine.
Pretty weird problem, and very annoying, like any FPS problem is annoying. I sympathize.