please post an image

Sounds alarming, but keep up what you're doing and most likely it will be fine. I had potted guavas for many years, and cut them back severely many times (to little or no remaining foliage), and at other times they dropped many leaves on their own due to numerous reasons (sunburn, hail, etc.), and always they bounced back no problem, usually with lots of flowers and some fruit to follow.

As tasty as the guavas were, the hassle of dealing with scale outweighed the few fruit I got per year, so ultimately I threw in the towel on these. Citrus were the same story, now the only indoor fruiting plant I have is garambullo cactus. But then again, I could keep these outside at the most only 5 months per year in my climate (z6).

Good luck

Whats the cause behind wilting and dropping even young leaves

What to do to save my tree

Don't panic. Guavas shed leaves for any bit of stress they suffer, but soon recover the leaves. You will soon see fresh green leaf-buds appearing on the bare branches.