Sciatica can be caused by stress, in some cases. This can happen if the stress causes muscle tension, spasms, or knots in the lower back, buttock, or leg, which can affect the nerves and cause pain, numbness, or weakness. Stress can also affect the immune system, and make the body more susceptible to infection or inflammation in the lower back, buttock, or leg. To reduce stress, you can try some relaxation techniques, such as breathing exercises, meditation, yoga, or massage.