random feelings of despair and dread?

i’ve been on medication for 4 years now and it has changed my life drastically. i suffered with mainly anxiety but also depression as well, and i am so much happier and less anxious now. on random days, often when i am sitting by myself or when its a gloomy day outside, i am overwhelmed with an intense feeling of just dread and wondering why am i even alive? after not having bad thoughts for so long, these scare me pretty bad and i am afraid to tell my family about it as they don’t need to worry about me, we have been though a pretty intense trauma over the past 3 years due to my sisters cancer treatment and her eventual passing. its like something deep inside takes over my brain and just goes “you need to die, something horrible is going to happen/your life is going to be full of pain and horrible things will happen to you if you stay alive.” i’m not going to act on these thoughts, i just don’t understand why this is happening. does this happen to anyone else? does this mean my meds are not working as well anymore? i just want to see if anyone else feels like this sometimes and how they deal with it