Is it normal to get flashbacks?

I think of things that have happened in the past and events that are going to happen and I get depressed. This happens occasionally and when this happens I see myself channeling all the aggression and suppressed feelings that I have onto other people. When I do this, I don't tell anybody what is going on with me and end up snapping at them for no good reason. After this happens though, I feel overwhelmed with guilt and start crying and shaking. It is weird that when I start shaking I always immediately think of the night that I overdosed and get the exact same feelings/symptoms. I can feel the numbness. I can feel the nausea. I even feel my throat loosening up the way it did when I vomited. Is this normal or am I going through something that other people aren't?