What is the status of torment after death ‘azab’ of suicide? Is it sin according to Ayat and Hadeeth? If yes, why is is a sin while no one willingly does this act but he does so when there is no option left behind for him or when he is mentally sick?

It is a sin to commit suicide. Islam will not say it’s halal because that would encourage many people to commit suicide. We believe that Allah is fair and will judge people with equality. If they are truly sick, and are not making proper decisions, Allah will only hold them accountable for what they know.