If your friend is experiencing difficulties with emotional regulation, impulsive behaviors, or dissociation, it's crucial for him to seek professional help from a mental health specialist, preferably one experienced in dealing with personality disorders like Borderline Personality Disorder (BPD). A proper diagnosis and treatment can help him understand his experiences better, learn coping mechanisms, and work towards healthier ways of managing stress and emotions.
Encourage your friend to reach out to a mental health professional, and if he's resistant, try to be supportive and understanding, as it can be challenging for someone with undiagnosed mental health issues to recognize their own struggles. If you believe he is a danger to himself or others, don't hesitate to involve a trusted adult, family member, or authority figure to help ensure his safety and well-being.