There's been a few times when I've cried over things unrelated to my dp/dr and my dp/dr actually mostly lifted for 20 minutes or so. My dp/dr is constant, so this really surprised me. I really do think that emotional expression is an important thing for us, although it's hard to go about it when we feel so numb a lot of the time.
I have wondered a fair amount about when crying seems to help and when it doesn't. For some people it's like a catharsis, whereas others will cry for weeks and nothing seems to change. Perhaps it's what you have in mind when you're doing it. Crying about dp/dr or symptoms in general probably doesn't help as it's too vague and doesn't give the mind anything concrete to work through, so maybe that's why you felt some relief when you were crying about something other than the condition. The reasons we might have been disturbed or upset to begin with might be quite mundane and due to various interactions with significant people in our lives. Then there's the question of whether you can target specific issues or if it's better that it's unforced and spontaneous. It also might be that crying is unhelpful if it's self-attacking, such as, "I'm a terrible person" when there might need to be some corrections made to help the process, such as, "I was made to feel bad, but I wasn't a bad person." (Aka, goodwillhunting yourself!)