Heel "locked", cannot walk

Sometimes if I have my foot in an extended position with my toes pointed straight out, the bones at the back of my foot (at the heel) seem to "lock" in a certain position, kind of like a dislocation. The result is extreme pain if I try to move my foot back to its normal position (perpendicular to my leg). I can't walk when this happens. It's been happening on and off for years now. Sometimes it lasts for a few seconds, and once it lasted for 4 hours. It's so humiliating to be limping around and since I'm clearly not disabled, I feel self-conscious that it looks like I'm exaggerating or making fun of others. To get it to stop, I pinch the area above my ankle on both sides of my foot and slowly move my foot back to its normal position, and this sometimes relocates the bones. If that doesn't work, I apply ice to the area. But sometimes that doesn't even work. Please help!

[melquiades]

oh, and I went to a family doctor who recommended I get an ultrasound. I had my entire foot an leg ultrasounded, and they never got back to me...meaning they found nothing.