There may be underlying causes that only manifest themselves when we are in those situations.
If you drive with a wallet in your back pocket, it can press on the area where the sciatic nerve crosses over the bony part of your hip and causes the nerve to be irritated, even pockets that have rivets, or are thick at the seams where sewn to the pants, can be a culprit. Another problem that can be a cause, and is generally overlooked, is fashion. If we wear a belt, of any width, or have pants, slacks or even sweats that have a drawstring at the waist, the problem may be the belt or drawstring is pressing on the sciatic nerve. A belt is the biggest offender when sciatica is a problem while doing manual labor. Suspenders may solve the problem, but they're out of fashion. We have to ask ourselves what's more important to us, not taking pain pills or wearing our shirt on the outside and over the suspenders. A slight constriction caused by a belt may not even be noticeable, but can irritate the nerve over a period of time.
Tight pants, slacks or skirts with elastic in the waist, a shirt that's not flat where it's tucked into the pants or any number of things that constrict, rub or are tight between the bottom of the rib cage and the middle thighs can be an offender .
Most of the people I talk to that have problems with sciatica, have it after riding long distances in a car, sitting in a chair for long periods of time or doing some form of work that is out of the ordinary. If our work requires long periods at a desk or sitting, the sciatica may be from poor posture, too hard a chair or a chair that puts most of our weight on the upper parts of the legs or the tail bone, and not on the sits bones. Sciatica from sitting in a car for long periods can be from poor posture or from excess weight around the middle which can pull the lower back out of proper spinal alignment. We may also find we suffer pain in our legs after doing work that we're not normally used to performing.