Astigmatism means your eye has to choose or compromise between focusing either horizontal or vertical lines. If you've got a flat plane of a repeating pattern maybe it makes your eye flip out, trying to figure out how to focus on it. Astigmatism can also make straight lines appear to bend, move, etc. If one eye is more astigmatic than the other and you've got a lot of parallel lines, it's possible that when your brain stitches together the left and right eye you might get some sort of moire interference pattern. Does it help to close one eye?
Flicker vertigo, sometimes called the Bucha effect, is "an imbalance in brain-cell activity caused by exposure to low-frequency flickering (or flashing) of a relatively bright light." It is a disorientation-, vertigo-, and nausea-inducing effect of a strobe light flashing at 1 Hz to 20 Hz, approximately the frequency of human brainwaves. The effects are similar to seizures caused by epilepsy (in particular photosensitive epilepsy), but are not restricted to people with histories of epilepsy. This phenomenon has been observed during helicopter flight; a Dr. Bucha identified the phenomenon in the 1950s when called upon to investigate a series of similar and unexplained helicopter crashes. Flicker vertigo in a helicopter occurs when the pilot or front passenger looks up through the blades of the main rotor as it turns in the sun causing the light to strobe. The strobe light effect causes persons who are vulnerable to flicker vertigo to become disoriented, lose control of the aircraft or have a seizure. A similar situation can occur in fixed wing flight whenever flickering light conditions exist. An example would be looking through a slowly spinning propeller while the airplane is landing facing the sun.