I am sorry your fear of death is overpowering you. As VelvetGreen says, it is an understandable and natural fear but it shouldn't take over your life!
I know you say you are not sick but has someone close to you died or been seriously unwell? Thinking about the mortality of others can bring with it thoughts of our own. If the fearful feelings are seriously encroaching on day-to-day life, some counselling might be beneficial to try to find out if there is anything that has happened or is happening in your life that might be a trigger for your feelings.
I sometimes contemplate death and worry about leaving behind those I cherish – just as you do. My DS is still quite young and I want to be here to care for him. And I hope when my time does come that I will have done enough to leave a warm sustaining afterglow in his mind that will stay with him throughout his life.
Of course, none of us knows what death feels like or if fearing it is reasonable. However people who have had near death experiences (NDEs) usually describe their fleeting encounter with the early stages of death as positive.
I knew someone who had a heart attack. He went into cardiac arrest on the operating table and had to be resuscitated. His personal experience of the event – his NDE – involved him looking down from a vantage point in front of and above his own body at the doctors working on his body in an attempt to revive him. He felt surprisingly calm and happy for someone who was detached from his physical self according to his own subjective experience. For him, the incident removed any fear he had of death.
There are many similar stories of NDEs out there, some quite detailed. Reading some of these accounts might make you feel less scared. Some would argue that the experiences are not real in any absolute sense – they are just the strange last offerings of a dying brain. But subjective experience is all any of us have to go on when it comes to knowing reality and NDEs are real - often hyper-real - to the experiencers.
A lady called Anita Moorjani had a particularly vivid NDE.
If you listen to her being interviewed, I think – and hope – it might steady you.