回忆起不该回忆的回忆
[huí yì qĭ bù gāi huí yì de huí yì]
'Memories should be left forgotten' would closely capture the sentiment of '回忆起不该回忆的回忆'. This phrase indicates reflecting on memories perhaps best left in the past - ones that could cause distress, regret, nostalgia, or unresolved feelings if remembered again.