Aussie, that is quick back to work and the sitting, I bet there are inflamed nerves to the muscles that sent unhappy signals.
The nerves are recouping from surgery poking proding, then the sitting, the muscles sound like they spasemed to create a brace, or splint, wrapping around, thus the spasm and jolting pain.
it is a catch 22 , if you stand too much, if you sit too long, try to break up the sitting frequent stand and mild stretch like a yawn. BRING your feet up from the floor too. The hanging legs can be a contributor.
Lean to the wall back against it,
Do you have a good lumbar cushion or support, I have one of the mesh ones I take with me and then at home I use a foam molded in the recliner.
Any one position for a long time is going to be a problem.
My last spasm, I had to fall sideways onto the bed, get the knee to chest and let if fall a bit to the opposite side, Hot shower bent over letting the hot water just hit it. BIOFREEZE, knead the spot, moist heating pad. or ice, try both.
But it seems the work chair needs some help, and breaks in position. I would not worry much about the re-herniation as much as inflammation. You did not have a new fall, or accident, just a huge flare up.
If you are in a tight mode too, flight or fight, tense, tensing the muscles, it does not help. Relax, think of each limb relaxing and support under the knees,
I tried one day to kneel and lean over a huge play ball that dgs has, that let me stretch gently and rock to loosen the stress from a long drive.
The driving is killing me with new work I am doing.
I use valium for the truest muscle relaxant. Nothing else seems to help.
You are still recouping too so be gentle, and relax, focus on the spasm relaxing its nasty grip.
Hope it improves, keep an eye, if something really feels not wrong, always follow up at the surgeon,
Best hearing from his mouth, the second guessing.
di