With the extra history, then yes it would be your lower thoracic spine (TSp). Of the signs and symptoms the only ones that would be regarded most serious would be the umbilical area numbess and the reduce reflex (response) in the lower limbs.
The latter could also be caused be the cocktail of drugs they had you on by then, unless they were reduced prior to that.
Did the MRI not include the lower thoracic area, then cos that's where you'd expect the problem to be given the above.
Sounds like you saw a good physio. Was it the lower TSp that they manipulated?
And did this help or do you think that it was solely the hyrotherapy that helped?
On the info given I suggest that the most likely problems would be either a facet joint lock in the lower TSp, or a disk injury in that area. The latter is less likely if they scanned that area and found nothing, but it wouldn't definitely rule it out. I'll explain.
If a disk is just herniating (also called bulging disk) and has not fully prolapsed, then it's quite possible that when your lying down for the scan, then it takes some of the pressure off it so the bulge may reduce to appear normal. [&:]
Another differentiation between disk and facet joint (but not definitive either) is the length of time of recovery - disks usually take longer. From your recovery time it could be either.
As to why it happened - most often it seems that these things are just waiting to happen, then doing something relatively minor, like picking up a feather could finish it off. [
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If it was a disk, then it maybe that you're susceptible to disk injuries (don't know age, etc), but there are things that can help on that front, if that's the case.
Why was it so severe? Probably because it was so close to your diaphragm and anything threating in that area is percieved by the system as threatening your ability to breathe, so system can go into panic stations and overload. []
Andrew.