Have you ever tried pushing through the anxiety/fear/whatever this is? I ask because I have sometimes had a similar reaction. I remember my first few jobs, I would burst into tears after an offer was made. Before going on big trips, I would get very anxious and want to cancel my flight.

Usually, these strongly negative feelings go away on their own, once I see that the thing I was dreading is not so bad after all. Maybe the same thing will happen with you and your new job.

Travelinglady has some really good points -- try to figure out what the specifics are of what is making you so upset about this situation and then do something to change it. Your schedule does sound like a bummer. Could you continue looking for a job that has hours more to your liking while you are working this one?