Normal
I've noticed that stirmis and blondies often have that bald spot, it's not necessarily from stress, though it could be. I'm of the opinion that they just like to throw their urticating hairs all over around their domain, as a warning, or a defense. I could be wrong though. It's hard to judge why tarantulas do what they do...I owned a mature male wild caught stirmi that died naturally, about a year after I got him. He never kicked hairs at me, but he did stridulate if my hand got too close and he was in a mood..I always thought it was cool when he did that I miss that big boy.