Why is my speed graph so high?

Hello, this is something that happenes to me every once in a while and I have no idea why. 
As shown below, my speed graph just becomes really high for some reason and it's gets a bit annoying to edit this way since I can't see the whole graph properly. I'm not doing anything different with my keyframes so I have no idea what's causing this. 
I'd love to know if there's a way to fix it, or at least understand what's causing this. Thank you.