Depending on what car it is, there are solenoids that shift between modes in the seat transmission. You may have one of those bad or a poor circuit or even a bad switch. It would need circuit testing to find out what is causing it.
Sorry. I did not try to get too technical. Basically it needs to have a professional diagnose it. It is not something you can just say "Do this" and it will work. You do want to make sure there is nothing under the seat that could be jambing it. If you get up to Kalispell, we could diagnose it for you at Loren's Auto Repair.