Side effects - What's up with SWIM's cannabis?

[Pseudo-leipä]

SWIM is a regular weed smoker, and has got very heavily stoned before and loved it. No matter how much he's smoked, he has never been sick from weed.
Yesterday, SWIM was stuck at home and bored, and so rolled a relatively weed-heavy joint. He hadn't smoked anything from this batch yet, but it was from his usual supplier. His friend had smoked from the same batch the previous night, and hadn't mentioned it being in any way unusual.
SWIM went into the garden and started smoking the joint, and after a few tokes started feeling surprisingly strong effects already. He started feeling really good, really high. However, by the time he had smoked about 2/3 of the joint he didn't really want any more, he felt a little queasy. However (foolishly) SWIM forced himself to finish the joint. He felt very lightheaded and quite ill as he walked back to the house, and as he climbed the stairs to the bathroom everything was spinning. SWIM then had to go to the toilet, and had quite bad diarrhoea. After this, SWIM just curled up in a ball on the floor of his landing and lay there, feeling quite sick. He also got a strange feeling as though his ears were bleeding: he could feel a warm liquid oozing out of his ears. Although the feeling was very real, he knew it was just some sort of halucination. He also experienced a lot of numbness in his jaw. While lying here, he noticed that his breathing was very rapid and heavy.
After a while he felt as if he was going to throw up, and so went back to the bathroom, but he didn't throw up in the end. Feeling slightly less ill, SWIM went downstairs again and made himself a glass of water, which helped the terrible burning dry feeling in his throat. SWIM was still very lightheaded and did not feel good at all, and also realized that he was halucinating smoke blurring his vision. However, when he tried to focus on this smoke it disappeared. He returned to his bedroom, and lay on his bed. SWIM told me he isn't entirely sure whether he fell asleep on the bed or not, but he definitely lay there for a couple of hours, unable to move without causing himself to feel very ill. While in this semi-sleeping state, he experienced some interesting dreams/halucinations. After a while, he found himself able to walk around without feeling sick, and from that point he was fine, with mild munchies and quite a euphoric high.

So, what happened? Quantity-wise, SWIM has smoked a lot more marijuana than that, and he has felt more stoned than that, and not felt ill at all. But never before has a single joint affected him so much. SWIM has three theories:
1 SWIM's weed is just a lot stronger than the stuff he usually has, and thus he took too much in one go.
2 SWIM's weed is laced with something
3 the tobacco that SWIM used in the joint was stale (this might explain the sickness, but not the unusually strong effects)

Anyone else's thoughts on the matter would be greatly appreciated.