Fear of death

I'm a mother and my oldest son just turned 5 and my youngest is almost 2 months already. It makes time seem like its going by so much faster and it made me realize how terrified I am to die, I've never been religious and or thought about what happens to us after we die but I have nightmares now where it's just nothing, like I just stop existing all together and that doesn't seem all that bad in theory but the thought of it just fills me with dread for some reason, and I can't stop thinking about it, every day for the past few months I have this feeling. I just don't know what to do, I hate feeling this way, I don't want to spend my life being afraid.