I have a 21 inch iMac 2011 with 8GB RAM. Initially I was very happy with el capitan as my machine was really smooth. With recent updates however I am noticing that the machine is initially fast but when I wake it up from sleep next morning the mac becomes very slow .This is a problem that I used to face with windows machines but not with mac. Apps take ages to open up and most of the time clicking on anything brings up the spinning beach ball. When I ran activity monitor I couldn't find what was slowing it down except that activity monitor itself used to show usage 25%. When I shut down the machine and restart it seems to be fine till I leave it to sleep overnight again . Can anyone suggest a fix?