Please note that I do not own these videos. Nonetheless, I found these videos to be helpful for understanding POTS.
http://www.youtube.com/watch?v=NN3PB6N6oGY
http://www.youtube.com/watch?v=I40-r3RpFjs&feature=relmfu
http://www.youtube.com/watch?v=PHydjGdg4XQ&feature=relmfu
http://www.youtube.com/watch?v=iJ9bv7jx-Ls&feature=bf_next&list=FLRRSwfzM-wyc&index=2
http://www.youtube.com/watch?v=7h9V8ryYMcg
http://www.youtube.com/watch?v=sTCLU7jwi7s&feature=related
http://www.youtube.com/watch?v=OTJ3x9erVBU&feature=related
Three-Part Series of Videos: (Recommended highly!!)
1. http://www.youtube.com/watch?v=Fx688XLvA8k&feature=mfu_in_order&list=UL
2. http://www.youtube.com/watch?v=bTM8RNzV6k4&feature=mfu_in_order&list=UL
3. http://www.youtube.com/watch?v=4rtcw23CFqo&feature=related