Has anyone been depressed about an inevitable future?

i just got back from my great grandmothers 95th bday party and all of a sudden it hit me that she may not be around in a few years or w/e u get the point and all this **** im over whelmed with in life now and next thing you know im hating life, no this isnt the first time this has happened to me ive been diagnosed with clinical depression etc. but was just wondering if anyone else has felt like this before