I'm not a mental health professional, but dealing with persistent thoughts about death and demise, especially in the context of a serious illness like lung cancer, can be incredibly challenging. It's important to consult with a mental health professional or a counselor who can provide personalized support. However, here are some general suggestions that may help:

1. **Seek Professional Help:**
Reach out to a mental health professional, such as a psychologist or counselor, who can provide support and coping strategies tailored to your specific situation.

2. **Talk to Your Healthcare Team:**
Communicate openly with your healthcare team about your emotional struggles. They can offer resources, such as support groups or referrals to mental health professionals, to help you cope.

3. **Support Groups:**
Joining a cancer support group can connect you with others facing similar challenges. Sharing experiences and emotions with people who understand your situation may provide comfort and a sense of community.

4. **Mindfulness and Relaxation Techniques:**
Practice mindfulness or relaxation techniques, such as deep breathing exercises or meditation, to help manage anxiety and stress.

5. **Express Your Feelings:**
Share your thoughts and fears with a trusted friend, family member, or a mental health professional. Expressing your feelings can be a cathartic process and may help you feel less isolated.

6. **Engage in Enjoyable Activities:**
Focus on activities that bring you joy and a sense of normalcy. Whether it's a hobby, spending time with loved ones, or engaging in activities you enjoy, these moments can be a source of comfort.

7. **Set Realistic Goals:**
Break down tasks and goals into manageable steps. This can help create a sense of accomplishment and control, which may positively impact your emotional well-being.

8. **Cognitive Behavioral Therapy (CBT):**
CBT is a therapeutic approach that can be helpful in addressing negative thought patterns and developing coping strategies. A mental health professional can guide you through this process.

9. **Medication:**
In some cases, medication may be prescribed to help manage anxiety or depression. Consult with a mental health professional or your healthcare team to explore this option if necessary.

10. **Create a Supportive Environment:**
Surround yourself with people who provide emotional support. Communicate your needs to friends and family, and let them know how they can help you during difficult times.

Remember, it's crucial to consult with healthcare professionals who can provide guidance tailored to your specific situation. They can work with you to develop a comprehensive plan for both your physical and emotional well-being.