My ntt hides along my drift wood all day and I had them for months now. Only time it comes out is to eat or attack my indo and then it swims right back to it.
typical normal bahavoire for dats. maybe you should get rid of the hiding spot. or add more fish to create more activity in your tank. Depending what you have in there already.
I agree with the above comment that it's normal behavior. Mine hid quite a bit until about 8". After 8", the bigger it grew the more outgoing it became. And eventually was out and about almost all the time.
if it makes you feel any better, my ST will sometimes lay vertically (head pointing at sand lol) alongside the FX6 intake for hours on end .. perfectly healthy fish but thats just how they are