Okay, so you are spinning backside... landing, over rotating, and then hooking your HEEL edge and smacking your head into the ground. Correct?
Let's make sure you truly understand frontside and backside as some people don't get it. Riding regular backside = spinning to the right. Frontside to the left. Goofy reverse.
Also, important to note: This is reversed for rails, namely because of how skateboarding identified rail/box tricks. A backside boardslide isn't because you spun backside or are facing backwards, it's because on a skateboard the feature would be behind your back.