A survey by Khalil et al. (2011) found that any aura lateralisation can be followed by any headache lateralization, although there was a tendency for headaches to be on the opposite side of the head from their preceding auras which was trending towards significance. On a few occasions I myself have experienced migraines, which always consist of an approximately bilaterally symmetric scintillating scotoma followed by a unilateral headache.
How might cortical spreading depression in both hemispheres of the visual cortex result in pain on only one side of the head?
Khalil, N. M., Nicotra, A., & Wilkins, A. J. (2011). Asymmetry of visual function in migraine with aura: correlation with lateralisation of headache and aura. Cephalalgia, 31(2), 213-221.