Some of these descriptions sound like fainting/passing out.
I know that on mushrooms and other psychedelics, I have certainly experienced the uncomfortable dizziness of low blood-sugar.
This could be attributable to the effects of the drug, or of casting prior to consumption - or both.
Before jumping to any conclusions, I would suggest considering the fact that all psychedelic drugs must be treated with respect, as they are extremely powerful and unpredictable.
Large doses, combinations, tripping in states of physical stress or fatigue (ie not having slept for a long period of time) can all contribute to complications, if they arise.
Psilocybe mushrooms may be a 'natural' and relatively simple (to procure, prepare, consume etc) source of psychedelic experiences, but like anything else, they must be treated with respect.
By that, I mean - just because they are generally 'safe' - this does not mean their use is risk-free.
I've never heard of, or witnessed seizures (or anything resembling them) on mushrooms - but I would imagine that any great risk of risk of seizures occurring would come to be known sooner rather than later.
Having said that, I do not know what the various risks (or health effects) of mould contamination - in picked wild or cultivated mushrooms would be.
It should be stated that if you are in doubt regarding mould contamination, that the shrooms in question should be discarded (much like mouldy cannabis).