There is a second normal version worth knowing so you do not mistake it for distress. An uro that feels threatened will open its mouth, puff up, hiss and whip that spiny tail at you, usually while backing into a corner.
The giveaway is that it happens when you approach or reach in, not while he is lying under the lamp. Mine does the full display if I move too fast past the glass and then goes straight back to basking.