sluggish/appetite loss

Question
Starting yesterday my cat wasn't eating her food (maybe a nibble here & there but nothing substantial).  I usually feed her 1/2 cup of Iams adult dry food per day.  Also, she usually greets me at the door when she hears my car pull up when coming home from work.  She meows her head off until I open it---the past two days she didn't say a word, just sat there waiting.  Every morning I also give her about 4 Pounce cat treats, which she has happily eaten on these "sick" days.  I woke up in the middle of the night one day last week and once last night, hearing her on the verge of vomiting (but didn't find any vomit).  She seems sluggish but I'm not sure when I should take this seriously and take her to the vet.  Other than that she still purrs/wags tail when I pet her.  Could she just be a little sick and I should stick it out??

Answer
I definately would take a trip to the vet if this were my cat.
1) Her behavior is out of the ordinary -- the way she is greeting you at the door is not her normal routine

2) She isn't eating -- a definate sign that something is wrong

3) she's sluggish

Do you need any more reasons?  Trust your gut feelings and remember its better to be safe than sorry.  

You are very observant and you know your cat more than anyone else and you yourself have admitted that she is not acting like herself.