Senior cat and steroid shot

So my 13 year old cat Fluffy has been healthy through most her life with a few minor issues here and there. About a week ago I noticed fluffy started having a cough and then she woke me up in the middle of the night a few days later coughing again, concerned about this I took her to the vet. The vet listened to her and said her heart and lungs were clear and healthy sounding and he gave her a shot of steroids called Depo Medrol. (If only I would have known how dangerous they were I would have never let the vet give this too her) He said it seemed as though fluffy had asthma. The shot was given to her three days ago, the first day she was completely lethargic and distant but the past few days she has been a little more like herself coming around the family but still continues to be lethargic and falling asleep wherever she lays down, I mean shes a granny but she never has been like this, she tries to socialize but often times seems even to tired to ask for attention or care to get it, her thirst has also increased, she is eating the same as before and her breathing is normal.

Im worried about her she is an old cat but she isnt acting like my spoiled princess. Sites online say thirst and lethargy are side effects of the shot but then I have read tragic stories where these behaviors signaled something much more serious such as diabetes or heart disease even death. How do I know that these are just side effects or if its more than that? When should her behavior return to normal if it is just side effects to the shot?

Hi and welcome to TCS!

I am sorry your kitty is not doing well. Has she had a senior blood panel? Allergies are often the cause of asthma and should be looked into (http://catinfo.org/#Feline_Asthma). 

No she has not gotten a senior blood panel yet, and thank you for the article.
 

I would recommend getting the bloodwork done and possibly finding another vet. Diet is a good place to start but you should rule other things out and the bloodwork should help with that.