Your achilles tendon is tightening up on your muscle. When that happens the whole muscle is shorter so there isn't the room for movement that there should be. You can release the tendon of your calf to get rid of the pain by doing this:
Achilles tendon:
While sitting and your leg on your lap, take both thumbs and place them side by side at about ankle height on the tendon on the back of your leg and apply pressure hard and hold. After 30 seconds slowly raise your toes up as far as you can, release the pressure but hold your foot there for another 30 seconds.
For best results relax your body first by taking a deep breath and exhaling the keep your body at ease.
For the charley horses I found that digging my fingers into mine made the pain stop right away and the cramp released a few seconds later. Only after that happened would I remove my fingers from the cramp.