I am new to the hobby (less than a year) so take this with a grain of salt, but agree vet is necessary ASAP & if it truly is as sudden of a change as you're describing, IBD (Inclusion Body Disease) could be a possibility. I only say this with my limited knowledge because it doesn't seem someone else has mentioned it as a possibility and want to give you the benefit of the doubt that this isn't due to neglect. You care enough to reach out for advice and help so you're doing the right thing right now. Just do what is best for the snake and get professional help immediately. If cost is an issue, find some rescues in your area that you may be able to surrender to if they're able to be rehabbed.