Heel spurs are characterized by what's known as start-up pain. This pain occurs when transitioning from rest to movement. For example, after sleeping, a person stands up and experiences a sharp, intense pain with the first step. Many patients report that the pain subsides after a few steps—they need to "walk around."
This is explained by the fact that when we sleep, the body calcifies the sites of micro-tears. This is a protective mechanism, strengthening the ligament, but in reality, it's doing the ligament a disservice. The fibers, thus "healed," become even less elastic, shorter, and more taut, making them even more vulnerable. When stressed, these fibers are re-injured, causing micro-tears, which causes acute pain.