Why does a person's mind keep imagining situations with problems that do not exist and continue solving those problems in the imagination? Why does a person's mind keep imagining situations with problems that do not exist and continue solving those problems in the imagination?
This keeps the person generally in absent-mindedness and oblivious of the real problems at hand and fails to solve real problems in life.
Is is any syndrome or disorder?
What is the solution?
IS there something like CBT/DBT/IPSRT that can make a change?
It sounds like you're talking about what psychologists and neuroscientists commonly call episodic future thinking or mental simulation. In this cognitive state, we simulate possible future scenarios, often pertaining to social interactions we might have, or survival situations. This allows us to pseudo-test hypotheses regarding the possible outcomes for an imagined scenario based on inference and the memories of our past experiences in similar situations. This may be adaptive if it allows us to prepare contingency plans for those scenarios, should one arise. We do this habitually, perhaps because there are so many possible scenarios to simulate, and the more we explore options and form tentative contingency plans, the better prepared we are for the world. It might also just be a rewarding activity in and of itself.
Absent-mindedness, mind wandering, or distractibility by one's own thoughts may be problematic if we are chronically distracted away from the present moment and the tasks that need to be accomplished at the moment. Mindfulness therapies may be helpful in training the ability not to let the mind wander and instead focus on desired tasks. Activities that require concentration may also train this ability, such as music performance. In severe cases, stimulant medication may be helpful, such as amphetamines or methylphenidate.
Regarding neural mechanisms for these states, there has been quite a lot of research and speculation in recent years on the interplay between two major brain networks, typically called the default mode network and the salience network. In functional connectivity MRI studies, the default mode network seems to be active during the state you described, whereas the salience network is active during focused attention on the external world and while completing a task. It may be that differences in how these networks have developed in an individual dictate the strength of their tendency to internally simulate rather than focus on the external world.
Here's a study regarding these networks and PTSD: Neural Dysregulation in Posttraumatic Stress Disorder: Evidence for Disrupted Equilibrium between Salience and Default Mode Brain Networks