Bottom of foot pain when walking after sitting for a while?

Plantar Fascitis. Generally pain on the bottom of the foot is the sudden stretching of the plantar fascia, a big band of tissue that connects the heel bone to the toes. At rest it is short and when you stand your foot arch flattens out and the fascia is pulled away from the bone causing inflammation. It generally does not go away on it's own. See a podiatrist for long term relief.
Plantar Fascitis. A band of tissue on the bottom of the foot that attaches from the heel bone all the way to your toes. It is short at rest and suddenly stretched when you put weight on it. It causes inflammation and does not easily go away without treatment. See a podiatrist to get help and relief. That is generally the most common reason for your particular complaint.