That problem just got Nitrowned.

Ahh, thanks man! Works great now. Will keep this in mind in the future!

What has happened is that the key repeat value value is set to a value higher than the normally allowed range. Normally you can set it up to 15 frames. (1 frame=1/60 second) Now it might be say 100 frames. One way to fix this is to decrease the value until it's down in the normal range. You can do this holding A and repeatedly tapping down and/or left until the values are down in the normal range. You will probably have to do this many times. The value will go down to 0 and wrap around a couple of times.
If you're able to back up the save and edit it in a hex editor, change byte 3FBA to 7 and 3FBB to 2 and the problem should go away.

As a total noob to chip, I'm experiencing all those delightful things that I hear happen to everyone.
And today, it was my DMG's batteries dying on me and after replacing them I realised my song was scrambled. That was fine, I went back to an old save.

What was strange though, is that no matter what I set my key delay to, it refuses to move more then 2 cells before (almost) coming to a complete stand-still. If I hold it down for ages it eventually moves, but it's long enough to be infeasible.

Is there a common fix for this I didn't find with a few google searches? WIll I have to reformat the sRAM?

Thanks for your understanding.