One week seems like a pretty short time frame for a blood to go from thriving to being on death's door. What other symptoms, along with the regurge (which is concerning), are you noticing? If it were me and one of my animals went downhill that quickly without any apparent cause, I would start wondering two things...was the animal really that healthy before, or did I miss/not notice something? or what kind of fast-acting environmental factors could be at work (e.g. cleaning solution that was used, possible injury from the mouse, etc.). I would think that even if your temps and humidity are a bit off, your animal would not go from 100% to almost dead within a week. Are there any RI symptoms? What is the age and size of the snake? How long have you had it? Pics of the set up and animal are always helpful.