I had hyperopia ~+5, had lasik. current 20/20 now i have to perform convergence exercise(pencil pushups), i feel bad vision if i discontinue it. why?

Muscle imbalance: You probably have had week eye muscles most of your life, but the effort it took to focus and see the world clearly before your lasik helped to keep your eyes aligned. Now, after successful lasik you have a tendency for double vision, a form of convergence insufficiency.

Convergence lacking: You have convergence insufficiency which should improve with the exercises. You may need to continue them indefinitely though. You should also get your cycloplegic refraction checked to ensure that your refractive outcome was optimized.