First off: don't feel too bad. The behaviour you describe is super-common and I think probably the norm, rather than the exception. Most people don't have to battle with it though, because they have regular jobs with commitment-reinforcing routines and regulations. What you need is to somehow get that same level of external "force" on you in this new running-your-own-business environment, where otherwise it is so eas…
Be warned though, this kind of intense visualization of bad consequences (or positive rewards) can also back-fire: if you start associating thoughts about your work with potential negative consequences it could drive you to shut down / try to distract yourself harder, and if you start daydreaming about positive consequences it could satisfy your reward circuitry and reduce your motivation. In other words, you have to…
Being mindful of future happiness definitely keeps me on track. But I think the core problem is that one's "body" has learned strategies for temporarily ameliorating stresses that are nearly impossible to talk down. One must simply deny the body the fix in the hopes it will reduce its chemical urge.