I have sciatica, which a recent MRI scan showed is most likely caused by a disc in the region of L5/S1 touching the thecal sac. Generally the symptoms are sharp pains in the region of the rump and behind/above right knee and behind above right ankle. This is generally aggravated by sitting for prolonged ( ~30 mins + ) in the same position and does relieve when standing. Physio therapy treatment involves gentle exercise to try and move the protruding disc back into position. I am currently taking a total of 1800mg ibuprofen under prescription from my GP to relieve the symptoms.
A recent diving excursion (max 12m, 45 min dive) was awkward initially whilst preparing equipment, but during, and post dive, no symptoms were felt, despite a prolonged drive from the dive site, and did not reappear for some two days, possibly due to the body being supported in a different manner, relieving the pressures on the nerve, or even the increase in ambient pressure having some effect?
This condition has been prevalent for some three months now, and I was hoping for it to clear before a forthcoming dive trip to Oman (Aug 1).
However this does not appear to be the case and I am looking for some medical opinion/advice regarding diving with this condition. My major concern is that whilst the recent dive did appear to relieve the symptoms, is there any reason not to dive with sciatica, or any precautions that should be taken or contra-indications to be aware of ( apart from obvious increase in pain ?).

Diving and water activities in general are no more detrimental to the discopathy likely to be causing your sciatic symptoms than land based activities.
Remember though that the lifting of any weight can aggravate the condition as well as certain extreme movements of the spine.
I advise you to be guided by your specialist regarding activity and weight bearing and relate his advice to what you have to do to dive.
You should also be aware that the symptoms of your disk problem may disguise a decompression illness and also be aware that if there is a compromised blood supply to a part of the spine this may be more prone to DCI.