Minecraft character crashes client on different computers.

On a (non Realms) hosted server, my character now glitches out the client, regardless of which computer I try to log in from. The client slows WAY down and all menus become equally unresponsive.

When I discovered this issue on my Windows 7 laptop I spent a while completely removing and cleaning both my minecraft and Java installs to no effect. Then I tried logging in as my character from a diferent OSX 10.7.5 laptop and had the same problem.

The problem occured after I had given myself the max movement speed potion effect for 10 mins to help a friend look for a base he had lost. Everything worked fine until the last minute or so of the effect and then the client started slowing down and glitching.

Help! I moved so fast I stepped outside of time!