Ix Tab is probably not a real goddess. Here's a good little abstract specifically addressing the question. For those unwilling to click, I will summarize: there is no Maya goddess of suicide, and reference to her can be traced to the writings of Spanish bishop Diego de Landa immediately post-contact.

Landa was a resident of Yucatan 1549-1579 and in his latter days the Bishop of Merida. He was a primary chronicler of Maya civilization directly post-contact. He is also a controversial and (to me, at least) repulsive figure, as in 1562 he burned every piece of Maya paper writing he could get his hands on -- and this was just about every codex still in existence. Everything Landa has done for our understanding of Maya writing, he undid a thousand times when he burned the original codices.

As for the iconography associated with the modern-day legend of the "suicide goddess," let's take a look!

This is the panel of the Dresden Codex which features the image commonly credited online as "Ixtab."

The image appears in the Dresden Codex on page 53b. Here is a link to the full online version of the codex. More to the point, here is a link to the section of interest. This part of the codex is sometimes called the Eclipse Table, as it has long been thought to contain astronomical data. It seems to span a recorded or projected 33-year period, including the dates of multiple putative astronomical events. (Source.)

The picture on 53b shows a Moon Goddess hanging by her neck from a sky band, the Maya visual convention for the sky. The Moon Goddess does appear to be dead; her eyes are closed, and her body is spotted in a way similar to the body of the Death God seen above her in 53a. Alternatively, she may be an unconscious captive. Given the placement of this Moon Goddess within the Eclipse Table, it seems reasonable to say the "dead moon hanging in the sky" is a reference to lunar eclipse. The "hanging" element is not so much about the method of death as it is about connecting the dead moon to the sky bar above. Accordingly, while images of graphic demise are common in Maya art, death by hanging is iconographically all but absent (see first reference).

So from where did we get this association of the hanging Moon Goddess with suicide? Probably from the depths of Diego de Landa's brain. Suicide by hanging is a much more common image in the Spanish culture Landa hailed from than it is in the Maya culture he was chronicling. I think the perception that this goddess has hanged herself is most likely just a Spanish misreading of Maya iconography.

I am not at all an expert, just a hobbyist, so I will gratefully accept any corrections to my rambling if an expert sees fit to stop by.