Confused at what is happening with these action potentials
Nice graph. What happens when you reach the top of the potential (when you depolarize the membrane) that you need to go back to a resting potential to be able to stimulized again. The membrane gets "neutralized" and this reaction often over-shoots and goes below the resting potential, which is quite normal. Before reaching the normal resting potential there will be no further activation. The Wikipedia article on the "Action Potential" contains a more complete explanation.