Things that you fear primarily because they could cause death (such as HIV, guns).
It’s fine to name something that could cause death so long as you’re not naming it for that reason; for example, you could name being lost if the disorientation of being lost is why you fear it, rather than the fear of ending up dead.
For me, it’s missing big opportunities in my life. Edit: to be more precise, I’m afraid my life will be dominated by fear itself.
that human beings will make the earth uninhabitable for themselves in my lifetime or that of my daughter. Or, uninhabitable enough that world-wide chaos ensues.
Being alone. I’ve never lived alone. Never been alone for more than a weekend. While I’m most terrified of my SO’s death (which I know you disallowed in the OP), it’s for the very selfish reason that if he dies before me, I’ll be alone.
Also, what I wish most for in the world sometimes is to be alone. To have a little yurt in the woods all to myself, with no one to see me if I want to dance naked in the rain and no one to be bothered if I sound my barbaric yawp to the trees.
Enforced loneliness. I’ve grown used to my own company, but there are always other people around, even if they’re at the other end of a telephone line or internet connection.
I suppose a living death is ruled out - being so damaged that death would be a release? For instance if I became deaf, blind, dumb, and paralysed.
I’m not afraid of death, but I’m afraid of being dependent. I’d like to go like my paternal grandma and my maternal grandpa did: from “how can anybody that age be in such good health”, through a series of ministrokes which left them weakened but able, to the final one, in about 2 years. Enough time to leave their business in order and for the family to get the message, but neither dependent nor in pain nor bedridden.
It’s very selfish. I’m afraid that my presence in the world does more harm than good. That people actually dislike me and think badly of me or see me as a liability, or that I don’t have anything useful to contribute to society.
Another vote for disability and especially Alzheimers. My mother has it now and it sucks but at least she has two sons to look after her. I have nobody. I keep telling myself that I could kill myself before it gets bad but that’s easier said than done.
I fear experiencing the lead-up to a violent inevitable death. In other words I fear the fear of death. I think that would be allowable by the OP because I’m not talking about fearing death itself: I am not afraid to die.
I’m talking about experiencing the primal terror you get when your reptilian brain tells you that you are about to die - what Scylla described when he waterboarded himself. I’ve experienced it twice and it is inexplicably awful. I hate the thought that I would ever experience that again.
Dementia terrifies me, too, far more than death. Or it did, anyway. I’ve since made the decision that, if I were ever diagnosed with a progressive dementia, I would kill myself. This actually makes dementia a much less scary prospect; it makes dementia a fatal diagnosis, but plenty of things are fatal - cancer, car accidents, heart attacks, and so on. The decision to kill myself if ever diagnosed with a progressive dementia means that I will never need to watch the gradual, inexorable erosion of my own personality and intellect - even if diagnosed with an early-stage dementia, I would simply continue as more-or-less myself until the day I stopped. I find this reassuring.
I should note, lest any well-meaning Dopers feel compelled to seek help on my behalf, that I have not been diagnosed with a dementia; I’m a young man, and expect I won’t have to deal with this issue for many, many years (if ever). Nor do I intend to off myself for any other reason; I simply see no point, in the event of this particular diagnosis, in riding things out to the bitter end.
I should also note that this is my view - I’m not saying that all dementia patients should off themselves. People make the choices that are right for them; if someone else does want to live with dementia, that’s absolutely their call.
I have a fear of Asphyxia. I am fine if I know I will be able to breathe eventually, and I am fine with dying, not even the least bit claustrophobic but it is the thought of trying to get oxygen into your lungs and either not being able to expand your lungs or if you can, get a full on lungful of water (does that happen or do you go unconscious first?) or a burning intake of super heated air. This is getting me a bit overwrought just thinking about it.