I understand how it feels. Death is something that we all have to grapple with at one point or another.
Setting OCD aside for a moment, most people fall into 2 extremes when it comes to worrying about death. On one end, many people distract themselves from it; avoiding the topic entirely. This is especially common in modern day society. We get dead bodies out of sight as quickly as possible. We keep sick and dying people hidden away in hospitals. People who talk about death are labeled as "morbid," "goth," "pessimists," etc.
This taboo treatment of death only makes it more foreign to us, making it that much more painful and shocking when we lose someone, or when we have to face our own death.
On the other end, many people worry about death constantly. They find it impossible to enjoy life because they know it will end some day. And obviously if you have the tendencies that are exaggerated by OCD, it easily becomes a full blown obsession.
It seems pretty bleak, right? You either ignore it and make things worse when it happens, or endlessly worry about it making things worse right now.
But there is another option, which is to acknowledge death as a natural part of life. Accept that all living beings die. Realize that it's not personal. It's not something that "happens to you." It's an inevitable result of living a conditioned existence.
That on its own probably isn't too helpful. I used to feel the same way; whenever people told me that death is "natural" and happens to everyone, I'd get annoyed because it didn't help me be any less afraid of it.
But something interesting happens when you purposefully reflect on the impermanence of life in a healthy way. When you truly accept it as reality, it starts to change from a source of fear to a source of pure inspiration and appreciation of everything in the present moment. You start to feel incredibly grateful for everything and everyone in your life. This feeling may come and go, but when it's there, little things stop bothering you. You feel more compassion toward people who usually annoy you. You enjoy your experiences more thoroughly. You smell, taste, hear, and feel things more vividly. You really feel alive.
The people that learn to do this; to live a life with the acknowledgement that it is impermanent; to be compassionate with others because THEIR life is impermanent; are the ones who feel a sense of ease and fulfillment as they near the end of their life, and they tend to face death without fear.
This extreme sadness and fear you feel is fueled by resistance. Those of us with OCD will literally do ANYTHING to resist our uncomfortable feelings. That's why we do compulsions; we desperately want to DO something to make sure we don't feel the feelings. But as we know, that makes things more intense.
When it comes to death, we may compulsively avoid it, or ruminate about it. Even ruminating about how scary it is can be a compulsion; it's an attempt to gain some form of control by staying on top of it at all times because we don't want to be surprised by it.
But the ERP approach is to turn toward it in a confident way. Acknowledge it. "Yep, one day I'll die." Allow yourself to feel the discomfort that brings. It's okay. Acknowledge it, then mindfully bring yourself to something in the present moment. If (when) the thoughts come back up, gently acknowledge it again.
Keep doing this. Notice how it makes you feel. If you find yourself spiraling, you've likely gotten caught in some thought-driven narrative about how death is scary and wrong. That's ok, acknowledge the spiraling thoughts and again come back to what's happening in front of you right now.
If you can learn to make this a habit, try to notice how your relationship to death changes over time. See if it starts to turn from a constant source of fear to one of appreciation and motivation.
I wish you well!