Problem, a crash, OR LACK OF CALCIUM. Need to get calcium into her asap . Or get her to a vet. I do not work with cresties, but have many other species, I keep calcium syrup on hand for any problems.

She will only grow weaker and go down hill fast, act quickly ! Let us know how she does, hope she can perk up and snap out of this. Has she layed eggs recently?
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PHEve / Eve