Why the jittery images
 

I need some help. I am putting together a video from this summer and when I watch it is is almost un-watchable in certain segments. I am using the same video camera that I have used in the past, a canon. Could my settings have changed? I like to slow it down to about 80-85%. the video is very jittery. The speed options are 24, 30 and 60i. Which is the smoothest? Also is zooming in or out better for smooth filming. PLEASE help if you can!