Just opinion. Different strains have different cannabinoid, terpene, and flavanoid profiles. Different people have different reactions. Most people react the same, but some will react different even when smoking the same strain. It has something to do w/ receptors in the brain. THC and CBD do degrade into CBN. CBN is what some think causes panic attack. There really isn't very much research on this. THC and CBD are supposed to counter those reactions or at least mitigate them to a manageable level. If the cannabis has degraded enough, those factors may be out of balance, or if the strain just grows w/ a high CBN content that could cause the panic attacks too.
In the eighties, there was some stuff they called Buddha Thai, and it was laced w/ PCP or opium. They called the joints sherms. That would cause people to have many different reactions, including panic attacks. It has always been better to grow your own, that way you know what you're getting each time.
I don't believe in tolerance being built. I have smoked some very nice strains and gotten pretty high, and have smoke some gnarly dirty ditch weed and still got high. I have been smoking since the early eighties. I have gone months smoking the same strain, w/ a few different strains thrown in once in a while at friends' places. The high is usually a little different, but I would not say the high was affected by tolerance. I would say that it is affected by the cannabinoid, terpene, and flavanoid profiles of the various strains and how they are grown and cured. I'm pretty sure the tolerance thing is just some other label for already too high, greed, desire, or some other mild form of self hate.