Some kind of exercise is essential in order to fully recover from your pain. Indeed, Exercise is recommended by the latest (2016) NICE guidelines for best practice, to be used alongside osteopathy for spinal pain.
Your osteopath will advise you on this, which may be as simple as just being a bit more active.
With things like walking a bit more, getting out of a chair unaided or doing a few basic exercises your mobility and muscle strength is restored, allowing you to get on with your life again.
But sometimes this is not enough.