Bipolar disorder tends to runs in families. Your father has it and therefore you are at an increased risk for developing the disorder. I cannot diagnose you over the Internet and just because your father has it does not necessarily mean that you do, but you might. If you do have it, this may explain why you find it fun and entertaining when your father is manic (i.e. you can relate). Perhaps he’s more “fun” when he is manic because being manic is like being high on drugs. Everything seems and feels better than it actually is. People with bipolar disorder commonly say they like the feeling of mania. Tara Parker-Pope’s Well Blog in the The New York Times last year featured a number of individuals discussing their experience with mania. One interesting quote came from Carter Goodwin, a 42-year-old artist with bipolar disorder, who said “I miss the mania…I love the mania. It feels so good to feel like I can do anything and like there is something really special about me. But it’s all chemical. It’s not true.”
You mentioned feeling impulsive while manic. Mania and impulsivity go hand-and-hand. If you are manic then you are not thinking clearly. If you are not thinking clearly then you are less likely to make well-thought out decisions and more likely to engage in less calculated or reckless behavior (i.e. impulsivity).
As for your brother, perhaps he’s concerned or embarrassed because he knows that the manic behavior is abnormal and unhealthy. To be manic is to be unstable. Some aspects of your behavior are apparently disturbing to him. That could explain his reaction to you and the reaction of others.
When your father is manic and you join in with him, you make be inadvertently making his situation worse. You take antidepressants for depression but you are not currently treating the mania-like symptoms (i.e. rushing thoughts, impulsivity). My suggestions for you are to realize that you are at risk for bipolar disorder (because of a family history), to limit or eliminate the manic-like activities that you engage in with your father, and to consider being assessed and treated for bipolar disorder. It is important to seek treatment as soon as possible so that you can decrease the chances of developing full-blown bipolar disorder. You may also want to consider family therapy. Since your father experiences mania, he may benefit from treatment as well. In addition, if he were being treated, it might make it easier for you to stabilize your manic symptoms. If you’d like to find a therapist in your community, please search this directory. I wish you and your family the best of luck.