I have found that some Crested Geckos (I have around 80) do tend to be a lot more ''flighty'' than others.

However if he is freaking while in the tank and your just moving around ,I would bet he needs more cover . He should feel secure enough in his tank to simply freeze and think you wont see him.

If he freaks when you go to feed him, that could be helped with a little handling each day.He has to come to understand opening up the lid isnt because its your feeding time and he wont be harmed.
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