The most common cause of heel pain is plantar fasciitis and it frequently causes an issue in the early morning for those afflicted by it. The condition results from repetitive stretching and tearing that causes a band of thick, fibrous tissue running along the bottom of the foot—the plantar fascia—to become inflamed or irritated.

The reason this is often so painful in the morning is because of a phenomenon known as post-static dyskinesia. What happens is that the torn tissue begins to repair itself during periods of rest, but is re-injured upon subsequent use. As the tears are reopened, the tissue becomes inflamed, which causes intense pain—not only in the morning after a full night’s sleep, but also after extended periods of sitting or resting.