... I'm wondering how many of us suffer from this sort of- post partum depression thing- after an event of this sort.
Everyone does - its normal. You mentioned being dumped by your gf earlier, well here you were dumped by your employer. Regardless of right or wrong, personal or not, the emotions are the same and everyone suffers them. The solution is to put it behind you and move on. Time will heal the wounds. BTW I've been "let go" from four different jobs for four different reasons over 25 years or so. The last one was just as painful as the first, but each time I got over it and moved on to something better. So, good luck with your next adventure.