could be arthritis in the heel of your foot try keeping a rolling pin by the bed before getting up take your feet and rub on the pin for about five minutes my doc told me to do this it helps me some. Maybe go to your doc and have an xray there are meds you can take good luck..
Google "Plantar Fasciitis" and see if you think this matches what you are feeling. This is an inflammation of the plantar fascia near your heel on the bottom of your foot. It is very common to have pain upon the first few steps of the day, or after sitting or laying down. See a podiatrist if simple measures don't help to relieve the pain. (ice the area 4 times a day, take Motrin if you have no other health issues, etc. The
rolling pin idea is actually a good one. You can also take a frozen orange juice can, and roll your foot on that.