Well, here's the theory on that. I do sit in an office and car all day soaking up stress, then go immediately to surf. That creates lower back problems. Plus, as mentioned, a lack of thoracic spine mobility effectively transfers strain from where the T-spine would take it to the lower back. Add in a heavy paddling arch and the twisting involved in laying down turns, and a lot of strain is applied to the L5S1 joint. Add in that the problems started during a period of heavy lifting and it's not far-fetched to think that a deadlifting injury occurred, followed by just enough repeated stress on the joint to keep flaring it up.
However, your skepticism is correct. My L5S1 joint is fine. The problems I'm having are from pelvic floor dysfunction. It seems that any time I do a core bracing activity - lifting, paddling, squatting on the board to turn, etc - I squeeze the pelvic floor muscles along with the abs. After a while, they get sore and too tight and pull other sh!t out of place. Sitting too long also exacerbates it. The PT is mostly focused on retraining to brace the abs without the pelvic floor and relax the latter, and it's working very well. Some exercises still cause an almost-instant flareup of pain - and the ones that do are not at all the ones I would have expected - but the general trend is positive, and I can surf with much less pain now than several months ago
And yes, Von Meister, I value myself enough to take a break from lifting, which I've been doing regularly for a decade and which will remain a lifelong activity for me, in order to get my body functioning correctly again. Although, given that many of the PT exercises are simply bodyweight lifts, I guess I haven't quit lifting as much as temporarily changed my routine.
You don't have pelvic floor disfunction....or you do and just left out the part about not being able to hold your bladder or bowels. Have you recently given birth?
You have an imagination of what's wrong because recurring pain is frustrating and now you have a hyper sensitivity to benign neural inputs. You also have a PT that is selling you this garbage as a way of keeping you on a routine that makes up a steady source of revenue.