I'm by no means an expert, but a few thoughts come to mind.
First, perhaps the symptoms are a result of prolonged inhalation to Butane

When lighting up cigs, it's a very short burst of Butane, but when firing up rips the flame and Butane exposure is much longer.
Second, perhaps it's the type of plant strain

There are so many available at the dispensaries. They even have Hybrid strains now.
Third, the potency is astronomical in comparison to the stuff being cultivated during the 60's.
In today's market, you now have "concentrates" and here may lie the issue. These are the edibles, gummies, cookies etc. Dab, hash, and oils that leave flower in the dust in the category of strength by comparison of THC content.
No matter what one's preference is, anything in excess above the level of moderation can be bad for one's health and well being.