I doubt this has anything to do with PAH. It sounds like soft tissue inflammation of either the achilles tendon insertion or plantar fasciitis. PF is most often felt on the plantar surface of the foot but it can extend upward around the heel. I would not go barefoot at all. The best shoes are a good pair of running shoes which reduce the biomechanical stress on the tendons. You do not have to do anything to get this kind of inflammation. It is amazing that I have seen so many sedentary people get it just as well as athletes. Gentle ice massage with an ice cube can help reduce the inflammation. Be careful on how you climb steps and how you go down steps. Most people feel worse in the morning but it can also feel worse after a long day on your feet. Before you get out of bed try gentle massage (without ice cube) across the site where it hurts.