sick as a dog 

People often associate a sick dog with eating grass and vomiting globs of whatever.

I drank too much last night and spent an hour with my head over the toilet bowl, sick as a dog!

sick as a dog by talk2me-JCH2 June 19, 2023

Sick as a dog 

Term for being incredably under the weather. Often used when trying to get out of something such as work or school.

The term came to be because dogs are notoriously constantly ill.
see sarcasm

Fred: I can't come in to work today, I'm sick as a dog.
Jane: Too bad... have a nice trip to the beach!

Sick as a dog by Dame ZNEK January 5, 2009

I’m sick as a hairless dog in the winter time 

When you are really sick and need to make sure everyone knows it. Phrase was created by a man that goes by the name of Lonestar Thompson.

“I’m sick as a hairless dog in the winter time” says Nathan

I’m sick as a hairless dog in the winter time by Lonestar99 March 19, 2021