vmstat -S display si and so. si is swap in pages. i.e no. of pages swapped into the memory. so is o. of pages swapped out to the memory. If so no. is very high, your systsem is swapping and subsequently will slow down more and more.
Also look at the output of swinfo -tam and if all swap space is used, you will experience that system is very slow. Also check with glance -m and look for memory available. If is very low, you are experiencing the memory bottlneck. You may need to put some more RAM on system.
There is no substitute to HARDWORK