You need to contact your vet about this.  It could be any number of
things causing the problem.

Nan

Some minds are like concrete, thoroughly mixed up and permanently set.

What it is is a matter for a veterinarian.  Please don't wait another day,
this could potentially be very serious.

Dee

Take your cat to the vet asap! This is a matter of life or death!

Unfortunetly nobody can tell you this unless is a proffessional and can see
and feel the cat. I strongly reccommend you take it to the vet at once.

When my neighbours Poppy started loosing weight rapidly, it turned out she
had Intestinal cancer. She died as there was no remedy.

On the other hand, when my Tiara started loosing weight, it turned out to be
a "fat lip syndrome" which caused her pain when eating so she'd just lick
the food a little then go. She was cured with some antibiotics.

Sleeping and letargy suggests she may even have a temperature, or is in
pain. Please take her to the vet now.

Gee

Take the cat to the vet and have things checked out.    
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