I also have heel pain too.My right foot only,and yes,especially after sleeping,and sitting off the foot for a period of time.
I absolutely cannot put pressure on my right heel in the morning,for at least 5-10 minutes.
It is a gradually applied pressure I have to do to be able to walk fully on my foot.
It is extremely painful,and frustrating.
I have had this problem for about 6-8 months,and it came suddenly one morning,and has never left.Once I am ‘up,and gradually walking on it,it is like nothing is there,I could walk miles and miles,but seems to be only when foot is sedentary,and not in use for awhile that it is back,and I have to walk on my right toes first,so please if you can also help me too,I would be grateful.