Is it possible for a traumatic experience to affect my feelings and behavior even when it isn't on my mind?

Yes. The mind does not forget anything. It grows and learns from it, but everything about you can be altered in some way or another, deteriorating your stability or rerouting the neurotransmitters or receptors in the brain.

Any experience and of course a traumatic one can create a long lasting change to a person's feelings and behavior

Trauma can take many shapes and forms. Sometimes things that aren’t necessarily related to the trauma itself l can trigger feelings related to the trauma. When I experienced a traumatic event I felt myself distance from everyone and lose focus, even when I was not thinking about the trauma. The effects of trauma can be invisible, and so it can be difficult to know when it’s on your mind and when it is not. Additionally, I would find myself in arguments with people that there was no need to be in an argument with, but I soon realised that it was my way of coping with the trauma I had experienced. It is completely normal to feel this way, and always a good idea to speak about these feelings.