Well, all I can say is best not to watch this movie if you're a bit depressed! It's a bit of a throwback to the early 80s really when there were several movies and TV dramas like this: THREADS and also the wonderful cartoon by Raymond Briggs WHEN THE WIND BLOWS.
Low budget movies after get mocked, but this is good enough and uses limited locations and minimal special effects to tell an end of the world story which is mercifully short.
And anyway, what would former child stars like Edward Furlong (Terminator) do without gigs like this!
Maybe watch together with the equally depressing THE ROAD, but then watch the best move of this type 28 DAYS LATER (or the scary late 1970s thriller about a disease wiping out the population) or DAY OF THE TRIFFIDS.
Then cheer yourself up with SHAUN OF THE DEAD!