I hate to bring it up, but is there any possibility someone other than you touched your savannah?
Someone else in your household or one of their friends may have taken the monitor out and dropped it or something. I would hate to say someone could have been mean to your lizard, but usually they get tamer and kinder towards people with time, not worse.
Did something fall on him in his cage? does he have a splinter from substrate/cage decor? Did he hit a lightbulb in his cage and get a burn?
He could be injured & doesn't want to move.
Just investigate the possibilities of what went on around the time of his attitude change. I hope the best for you and your lizard! Good luck!
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Melissa and Corny the Corn Snake
and Monaco the Argentine B&W Tegu
and Meanie the Black Throat Monitor