The temporal loss of sight and sound is called syncope or brief fainting spells. It can actually be quite dangerous. It happens because your body is not able to deal with the high dose of alcohol. It might be a good idea for you to stay off alcohol. The greatest danger is if you faint and suffer a head injury.
For allergies, it can differ from person to person. Most people who have allergies might not even realise that they have it. The common allergies that we see are itchiness in some parts of the body as well as rashes. The trouble is the rashes/itchiness might show up days after consuming the alcohol.