My shih-tzu is 11yrs old. There is nothing sprayed on the grass but when she gets a chance, she will nibble on the long grass that grows nr the fence. ( I pull any out that i see).
Everytime she does this she starts to hack and tries to be sick but nothing happens. She ends up very lethargic and it can last a whole day  and then she is  fine.
Any idea why she does this.   She did this yesterday.  She was fine when she went into the garden and a short time afterwards she came in a different dog.