Losing a job is so hard and there is a grieving process, so to speak. Experience and really feel the loss for a day or two (try not to binge -- just allow yourself 1 treat per day or something like that). Then try to start looking at your situation from another angle. Maybe this will open a different door for you and bring you a better opportunity than you had before? Maybe in researching/searching for another job, you'll meet someone new who might be influential in your life? I've learned you just never know what's around the corner.
After a couple of days of being down and sad, try to change your mindset and don't think of "exercising", but just go for a walk, alone, with a friend, doesn't matter. Walk anywhere, preferably outside. Go to a park or the ocean/lake if you have one. Walking outside will help get those endorphins kicking back in. Then make a pact with yourself to walk just 15 min/day and ease back into an exercise routine. If you can push yourself to exercise harder, so much the better. But when you go through something like this, even though you don't want to slide backwards, I think you should be kind to yourself too.
You'll get through this! Hang in there!