In response to the previous answer, contrary to what most of people think, a toxin is not necessarily out of their system once the initial symptoms have passed, some toxins are not metabolized nor flushed out by the body, they are just stocked in some organs and cumulate there. Another thing to considere is that even if a toxin is not in their system anymore, the damages it might have caused are still very well there, and could possibly be fixed.
That being said, if they have returned to their normal selves and that you cannot identify what could have caused it, it's unlikely that a vet will be able to do anything either, so by now, I would not rush to the vet, but I'd keep a close eye on them in the next days, and if they show any sign of abnormal behavior, then a visit to the vet would be indicated.
The symptoms you describe are quite general, lethargy and shaking can be caused by (without being limited to) lack or excess of sugar, alcohol, aspartam, cold temperature, stress or fear...
Used tea leaves do not contain much caffeine anymore, but they still contain theobromine (which is the alkaloid which makes chocolate toxic to gliders) which would cause seizures...