is it immoral to be mentally ill?

It is no more immoral than having cancer or diabetes. Morality issues are left up to what we can control, and mental illness is definitely beyond that realm

Is a character flaw?

Again, no, its not a character flaw, any more than cancer would be a character flaw for someone fighting cancer.

Does it reflect badly on you as a person?

Unfortunately, due to stigma, it DOES reflect badly on us as people who are mentally ill. It is our job to put a very "normal" face on mental illness to smash the public stereotype.

On your family or friends or co-workers?

If my friends and family are worried more about how the world will see them instead of my overall well being, they aren't the kind of people I want in my life.

How should people who find out treat you - with scorn or kindness? (Is anyone going to say scorn unless they are full of self-hatred?) Kindness, OF COURSE! Compassion, too.