A similar question has been asked before but for pepper plants. You can find it at this link:
I think Charlie B's answer on that post is a good one so I'll copy and past it ....
"Spider mites can hang aroung undetected for weeks, especially when house temperatures are relatively cool. Once they multiply a bit, it seems they explode overnight. Where did they come from? Usually they come indoors in the fall. If the plant was brought indoors, they probably were on it all along. If you have other plants, it would be good to check them for infestation too. What to do? It takes some persistence on your part - insecticidal soap helps but can take awhile to get results. You can speed the recovery by giving the plant a gentle shower (emphasizing gentle) in the sink or bathtub - this type of physical removal makes a big dent in the population. You can't really fix the damaged leaves, but the plant should perk up with some new leaves"
Also take a close look at the images - the stippled leaves are classic spider mite damage, you may also see webbing on the plants