Originally Posted by FBinNY

Before blaming the trainer, I'd suspect addle height.

I'll venture that the combination of body posture and saddle height had your hips rocking as you pedaled, putting twist into your lumbar spine and causing inflammation and pressure on the sciatic nerve.

Possibly the rigidity on the trainer contributed, but I doubt it would have caused an issue if all else were right.

Also, consider that many or even most people ride differently on trainers vs the road. Differences in cadence and pedal pressure, can change your style a bit, and that may have been the issue for you.