How to deal with this?

It sounds like whatever experiences you have had with trauma have caused you intense emotional reactions sometimes, but not so much at other times, so that your emotions hit you in an unpredictable manner. Since the impact of trauma differs individually, what trauma actually is differs. A person can be traumatized by anything from the death of a loved one to a history of abuse by a family member to the difficult termination of a significant relationship. 

At its core, trauma is emotional energy of the nervous system caught in the limbic system in the body, which regulates emotions. When the body is regulating itself, it moves between different parts of the brain to manage situations. Trauma sometimes has the effect of keeping the emotional part of the brain hypersensitive to stimuli by "trapping" it there, so that when trigger events occur, which can be normal things that remind the brain of trauma, strong reactions happen.

Trauma therapy takes memories that are triggered and reprocesses them so that the brain can move out of the emotional state and feel more relaxed. Several types of this therapy exist, including that which is done with creative means such as art therapy, dance therapy, drama therapy or other expressive therapies. 

EMDR is an example of a therapy that is decades old, but is now being used extensively. It's a combination of the free association of thoughts that arise in the conscious mind and bilateral stimulation of the right and left sides of the brain. EMDR stands for Eye Movement Desensitization and Reprocessing, and it is often recognized by people moving their fingers back and forth in front of their clients, like hypnosis. The back and forth is a left and right motion meant to bilaterally stimulate the eyes. Sometimes therapists also use touching the left and right arms or knees, or causing light to flash on either side of the visual spectrum, or by using buzzers in the hands, or even a combination of several of these.  Clients begin by vividly recollecting memories while being stimulated and seeing where their thoughts go. The mind, under the therapy, is guided to healing.

Depending on what has happened in trauma, it's important to set boundaries with people, especially if they've been responsible for some kind of abusive actions in the past. Often, people that are involved in abusive actions have themselves been abused and are acting out their own trauma. It's important to do our best to be self-aware of what has caused trauma so that we can perform the best self-care possible for ourselves.