THC overdose IMHO,
Heart racing, weak thready pulse, weakness, sweating, urge to vomit are typical symptoms.
Problem with strong cannabis is you can smoke a 1g joint in 10 minutes, but the effect takes 20mins to be noticeable.
If you don't know the strength of the cannabis, your tolerance or are inexperienced with smoking cannabis. Best to smoke 1/2 a joint then wait for 30 minutes if smoking alone, not really a problem if you're passing a joint around a group. If the joint had been 1/2 tobacco, you wouldn't have had a problem either.