Answer:
In my opinion, I think being happy and sad at the same time can depend on what just happened. Maybe its a extremely happy moment, and you start crying. So you are happy and sad at the same times. If your life does not have a extremely happy event, and you get happy and sad at the same time, it is a bit bad.
For the second question, if you tell someone with a valid reasoning, it won't be that you are a attention seeker. If you just told more than one person "I'm happy and sad" you are.