Obviously each person's experience is different. I 'tested' going off methotrexate once last year and didn't last much past two weeks before I went back on it. The original pain of my pre-diagnosis RA started to come back and that scared me. If you are trying/planning to stop methotrexate, work with your rheumatologist. He/she may prescribe you some steroids to help you with any pain and adjustment you experience. But definitely work together.
I can only tell you my own experience but I hope it helps. I came off Methotrexate after taking it for around 5yrs, I did worry that I would be in unbelievable pain once I stopped taking them and be so stiff that I wouldn't be able to move (you know how overactive the imagination can get) so I appreciate your concern. However once I stopped taking them I would say I experienced some pain and stiffness for about a week and then my body adapted. It was no where near as bad as I had feared. I hope this helps a bit but like I said it is my own experience.
As I mentioned before, I sometimes didn't take the methotrexate and possibly missing a week here and there helped prepare me for coming off it. I don't advise doing what I did, I was only young and didn't know better. I agree with Lisa that you should talk to your rheumatologist and see what they advise.