I think that memories are stored forever, and the emotional ways we were affected at the time stay in the 'sense memory', they can be triggered now and then by certain things and we become conscious of them again. You're right, I think that it is part of the healing process to have the 'flashbacks' sometimes. Somebody told me that these things usually only come back into our thinking consciousness when we are ready to process them. There's no chance of that happening when we are just numbing with chemicals.
Some people don't want the memories though because they are suffering from PTSD, there are some good CBT techniques for dealing with these things though, usually mindfulness and learning to 'stay in the moment' and recognize that there is no real present danger. It is worth seeing an expert in the field if it is a problem in sobriety.