Anyway, op, if your problem is personal, time truly does heal all wounds. It may take months or years, but the pain will one day be nothing but a dull memory, no matter how great it stings right now. What you must do till then is simply survive. Counseling, medication, religion, or your social support network can provide you with the strength to keep going until the pain fades. Pick which option you are most comfortable with.
If it is professional regret, time also ends to change your perspective. That C in micro or layoff might go from being one of the worst days of your life to one of your most profound moments of reflection, a catalyst for changing your study habits or work ethic that forever altered the trajectory of your life for the better. Picking the wrong career might leave you so discontent that it becomes your driving force behind going back to school and doing well academically, ultimately landing you the job of your dreams.
Ultimately, all things shape who we are, good and bad. Those awful moments serve to teach us lessons, and to make the good times that much sweeter by virtue of comparison.
Just do the best you can to care for yourself in the short term, and one day, almost out of nowhere, you'll realize all that pain is gone and somehow you're a better person for having survived it.