Hello again, and thanks for your reply with additional information.
If she's not drinking and her appetite and energy are down, it's possible she has a viral or bacterial infection in her system and/or that she ingested something she shouldn't have. She's also most likely dehydrated at this point, and will need IV or subcutaneous (under the skin) fluids from the vet. For the moment, you can dropper feed her some water--1cc every 20 minutes for an hour, then repeat in 2 hours.
It's also possible that she became injured jumping down from a height or falling off a piece of furniture, etc., which happened when you weren't in the room.
If she is not spayed, she may have a serious uterine infection called pyometra, which needs immediate treatment from the vet, but if she is spayed, we don't have to worry about that.
With the symptoms you describe, it would be advisable to have her evaluated by a vet as soon as possible, so the cause of the problem can be found and she can be treated. If your regular vet doesn't have hours today, bring her to an ER vet center for assessment and diagnosis, so she can start feeling much better, very soon.
I hope all will be well with your furry girl.
I hope you have found this answer helpful; if so, please click 'Accept' and leave positive feedback. If you need additional information, please click 'Reply'. Thanks for the opportunity to be of help.