Awakening from sleep is well documented to impair cognitive performance in young adults. This phenomenon, called sleep inertia, has been reported to impair performance just as much as one night of total sleep deprivation, suggesting that there are significant functional consequences to sleep inertia. However, whether walking stability is impaired by sleep inertia is unknown. If sleep inertia impairs walking stability, it could be an important but currently unrecognized risk factor for falls in older adults. Also, the impact of aging on sleep inertia-related impairments in cognitive performance is unknown.