Hello and thanks for writing to us. My name is***** am sorry you are facing this issue with your wife. Intimacy is an important part of relationships so I can understand that her lack of interest is concerning and frustrating.
So while ebbs and flows with intimacy in marriages is normal and often will pass with a little effort on both of your parts, the question about needing/seeking help really boils down to whether or not this is posing a problem in your relationship as well as why this is happening. I kind of assume it is a problem, or you wouldn't have written this question, so in that case, I think it makes sense that you talk to your wife about considering talking to a certified sex therapist about this lack of desire. You could join her in these sessions to explore ways to rejuvenate your sex life. It is possible that a condition like depression is causing or contributing to this lack of desire or it is possible she has just entered a new phase of interest which can be processed with a counselor and hopefully defeated. It is also possible that her lack of desire is reflective of other marital strains, and again for this, counselling is warranted.
Certified sex therapists can be found here...http://www.aasect.org.
For many women, a general decrease in sex drive is fairly normal and often reflective of external stress, however, once it gets to the point of causing trouble for the marriage, it should be explored. Hopefully your wife will be open to the suggestion of counseling and if she is not, hopefully you guys can work on the issue at home as a couple by committing to intimacy, even if she isn't really feeling up to it. Typically, the body will begin to respond to touch even if the mind initially didn't really feel up to it. So don't give up on each other! Keep seeking open communication with her so you can really come to understand her needs and wants but also so she can understand yours.
Also, if your wife isn't quite ready to dive into cousnleing but is willing to explore this on her own, there are a lot of books on the topic..
I hope this helps,