My 9 year old kitty has been vomiting (waking up from being aleep on my bed) between 3am and 5am every morning for the last two weeks. The same thing happened over a month ago and then abruptly stopped. The vomit is liquid and brownish in color. Every once in a while it has a small (dime sice) lump of fur in it. There has been no change in her diet. Any ideas on why this is happening? Thanks in advance.