Is forgiveness granted to one who commits suicide after suffering from mental illness or "possession," and is it permissible to perform Hajj, seek forgiveness, and give charity on their behalf, knowing that they were devout before their illness?

Taking one's own life is one of the gravest major sins. It has been reported from the Prophet, peace and blessings be upon him, that the one who commits suicide will be in Hellfire. Nevertheless, this sin is less than shirk (associating partners with Allah), and the one who commits it is under Allah Almighty's will; He may punish him if He wills, or forgive him if He wills, as corroborated by His Almighty's saying: "Indeed, Allah does not forgive association with Him, but He forgives what is less than that for whom He wills." The Prophet, peace and blessings be upon him, prayed for forgiveness for a Companion who had taken his own life, and Al-Tufayl ibn 'Amr saw him in a dream, and Allah had forgiven him. As for one who takes his own life while in full possession of his mental faculties, he is under Allah's will, and it is permissible to perform Hajj, give charity, and supplicate for his forgiveness. However, if he was not in his right mind, then he is not held accountable Islamically.