Dissociation is a normal experience at healthy levels and essentially equates to a simple daydream or forgetting where you left your keys. There are those with limited imaginations with which to daydream, whereas most will at the least, hold capacity to picture themselves on a vacation.
While boredom can play a role in reaching to escape in a daydream, so can isolation or social rejection. Escapism is part of the minds reason to reach to dissociate, as is self-preservation. In a traumatic event, dissociation can distance a person from an emotional response, make them feel like the event did not occur to them, or their memories of the trauma may be lost.
As an example of normal to disordered levels of something that can be healthy, or disabling, consider a condition like diabetes. Everyone has a level of sugar running through them, which is a normal and needed function, though, when glucose rises to dangerous levels, serious complications and symptoms result.
In that same concept, with triggers frequently brought on by trauma, the symptoms or results of this can vary.