Back pain can come on suddenly (acute) for no reason or from a trauma. Trauma can be a car crash, a fall or just a heavy bout of gardening when you're not used to it. Just overdoing things.
With trauma, you can be very fit prior but still need help recovering. If you cannot identify the trauma (most people) then this problem has probably been building up for some time and some ordinary movement has brought it on. An everyday movement such as reaching up, sneezing, lifting something not heavy or just a sudden movement can be devastating. At worst you can barely move either immediately or the next day and your body may have gone into an 'S' posture if someone looks at you from behind. This change in posture is a good thing as a compensation for the injury. It means your body has a good response to injury and uninjured areas are still able to adapt to help relieve pressure and entrapment from the injured area - often a disc bulge (slipped disc).
There is no point in trying to do back exercises when you can't move, so if you can't get to the clinic, try ice hourly for a few minutes each time preferably with a soft covered ice pack. This will take the swelling down. Move as soon as you can and keep moving gently and deliberately at first, building up until you can exercise. When you can get to the clinic you will need a set of sessions to find the cause(s) of your imbalance that caused the problem. These can be corrected to hopefully lessen the chance of reoccurrence. Following your treatment plan diligently should give you the best chance for a long-lasting recovery.
Everyone wants to know - 'How many sessions?'. This depends on so many factors such as , how fit you are, your job, your hobbies, lifestyle, diet, state of mind etc. Also where and to what extent the disc has bulged. Some directions of bulge are much easier to access and correct than others. And, of course, following your treatment plan and not missing sessions even if you feel OK. You may feel better but still be 'unbalanced' and on the threshold of it happening again.
Once you are feeling better, the sessions are gradually spaced out until a maintenance plan is established to keep you at your optimum. This may be monthly or up to six-monthly. Optimum varies for patients. Most patients are happy to stay at 80%. A top athlete will want to be 100%, for example.
Next, we'll see what 'chronic' back pain is all about.