Something happened and now I'm bouncing all over the world like it's a trampoline. What do I do now?
Try a relog; Log out of Second Life, and then restart the program.
If that doesn't work, try right-clicking on yourself and selecting Take Off > Detach All to remove your attachments. Then, try relogging. Scripted attachments have the ability to affect your avatar's movement, so always try to make sure you know what you are attaching to yourself!
If that still doesn't work, try unplugging your modems and routers for a full minute, then plug them back in and log back into Second Life.