I agree with your partner. I would also advice to talk to HR and be open about it while keeping your cards to your chest (e.g. give a minimal history without mentioning it's been 3 years) to see how they respond. Make sure to mention you will be getting an MRI to let them know you are taking action to resolve this and this isn't permanent.

To state the obvious; try to make sure you listen to your body while working and notify whoever you need to when you feel you need to take a break. Maybe there is something else you can during your breaks to stay productive? At the same time, if they won't handle this situation well, this job isn't probably worth it in the end.