iMac 21.5" late 2013 system preferences settings change suddenly

I have found that the dock suddenly magnified, even without the setting on. Then, when I tried to left click , but it became a right click on the screen, showing options for system preferences after I tried to open it. There were also a number of odd things that has happened. The screen saver was floating at first, and it changed to flurry. Another odd thing was that one time my dock suddenly disappeared. I found out later that the system preference setting automatically hide dock was on, although I did not select it. My iMac is running OS X 10.10.4 and has 2.9 GHz Intel Core i5, 8GB RAM and 1TB of storage.