Surreal Memoir

If you have multiple instant cards in your graveyard with the same name, and one of them is being targeted by another spell on the stack or is enchanted (with Spellweaver Volute, for example), you must differentiate them so you know which one (if any) is chosen at random. In that case, it may be better to use dice or another method that allows you to differentiate between the instant cards to choose one at random.

Surreal Memoir isn't targeted. You don't choose an instant card at random from your graveyard until it resolves. Once you randomly select a card, it's too late for players to respond.

If you cast a card from exile this way, it will go to your graveyard when it resolves, fails to resolve, or is countered. It won't go back to exile.