Hairball...?

Hi, we have a 10yr old female (DMH "Tabby") that has developed what we think might be a hairball problem. Prior to last month she (K.C.) never "gagged-up" hairballs. K.C. begins the "gagging process" only at times when she is sleeping. Nothing is ever puked up other than "spit" and occasionally food. After a week of this we purchased a tube of "Felaxin" and used that. A couple of days after treatment the "gagging" would cease and we would regrettably forget to continue use. We have made a more concious (Sp?) effort to give "Felaxin" twice a day and we will continue for a week even if condition improves. Appetite is good, behaviour has not changed, still very "bossy"
Continues to be playful/cuddly... Unsure of "litter box activity" as we have another cat. Unlike Kimba, the "stinky" one, K.C. is very private...Her eyes are clear, nose is moist...The other cat is fine.

Only one change in our enviroment and that was the use of scented candles during the festive season. That has ended and we're worried because of the "duration" of this problem. Should we "wait and see" if the regular medication combined with ommiting the use of candles cures the problem? See a vet soon? Or perhaps a different hairball remedy?
Any advice or similar experiences/solutions would be appreciated. Thanks in advance...
K.C.'s & Kimba's mom and dad

PS Aside from hi-tech video surveilance how do we watch her "litter box activity..."

The fact that she is 10 years old and you have never noticed her gagging, is cause for concern. I would take her to the vet if it continues. She could have something caught in her throat that is interfering with her.

The litterbox monitor is tough. You should have a couple of boxes for two cats. About the only way to observe litterbox habits, if you are worried, is to seclude the kitty in question for a day or so in a room with all the creature comforts.