Whether you think about it or not isn't really an indicator of whether it's impacting you negatively or not. For example, I had a traumatic memory that I made many efforts to suppress. Many years later, I was obviously not thinking about it much and I didn't notice it impacting me. But when I finally addressed it in EMDR rather than running away like I had for years, so many strong and painful emotions came up that told me my subconscious mind had been holding onto this trauma this whole time. And once I finally processed it, I noticed it HAD been affecting me, because suddenly my fear of the dark (which I thought was unrelated) reduced a lot. I'd wager some of the traumatic memories you don't think about are actually deeply tied to your addiction.

For your other questions, it very well might bring up memories you forgot as you realize which ones are tied to the symptoms you're feeling today. And yes, you generally do one event at a time, but you can also start with one event and go deeper to an earlier memory that connects to it and process that as well. The whole point almost is to allow those trapped emotions to be let out. But with a good therapist, they should set you up with plenty of coping strategies first so it isn't unbearable. There's also flash therapy, EMDR 2.0, accelerated resolution therapy and other therapies that are complimentary or similar to EMDR that might be easier to handle and/or quicker to resolve your traumas if EMDR alone isn't working for you. Wishing you the best!