Coccydynia is pain in the tailbone area (coccyx) usually caused by improper posture.
Slouching in the seated position puts much of your body weight on the tailbone. After prolonged sitting in that position, the tailbone becomes aggravated. Dull or severe pain can develop in the surrounding tissues.
The fix is simple: Sit up straight.
The problem is we may not feel it when sitting on soft surfaces like a cushy sofa or the bed. But the pressure is still there - the tailbone is still compressed and its joints and ligaments are compromised. The issue sneaks up on you over time.
Additional help: Perform strengthening exercises for the Glute Maximus such as the Donkey Kicks below.