Well... in the world of behavior theory... I believe this strategy would be referred to as "aversive reinforcement". Aversive reinforcement is seldom, if ever, appropriate. Typically what one would want to use would be positive reinforcement... in other words... if you get X done... you get something you'd like to have. The greater the value (for you) of the positive reinforcer the better. And then in addition to this, it's even better if you can establish both short & longer term goals & reinforcers. So you reward yourself with smaller positive rewards along the way for accomplishing smaller tasks. And then, at some point, you give yourself a bigger reward for having accomplished a bunch of stuff over a period of time. Does that make sense?

Threatening to cut yourself if you don't get something done is, it seems to me, nothing short of self-abusive. And continuing to use this strategy over time is, it seems to me, likely to lead to increasing levels of depression, anxiety & fear. So if you simply cannot figure out a way around this aversive reinforcement schedule you've created for yourself, my suggestion is to talk this situation through with your counselor or therapist if you have one, or get with one if you don't. One thing they might be able to do is to help you to develop a written schedule, or calendar of things you need to get done along with the dates by which they need to be completed. That might at least help you to be able to see what's coming due. And then if you can plan for some of those "positive reinforcers" along the way, so much the better.