Is there a community in Australia just like Ask, only for serious stuff?
say like, mental illness, or depression etc...
No, but there are quite a few Australians on Ask. You can usually get answers to questions about life in Oz. There's any amount of serious content on Ask. A lot of the sillier stuff was removed following a recent re-write of the community guidelines. But there's a lot of laughter, too. Enjoy.
Not sure, but try asking a serious question on here. I take a medication for post traumatic stress disorder and depression from a car accident that I was in.
You can ask serious questions on this site and get appropriate answers.
You could probably find a forum for a specific illness. Just google the illness + forum and a bunch of links will come up. I do not think there is any site devoted to only "serious" issues. You can always go to your settings and filter out the categories you do not want to answer questions in.