I have my 2 cens to share, old pp always said dun always go out at night if not we will get sick easily because too many 'dirty' things on the street night time.
In superstitious explain ghost do come out lot at night and most of us will walk through and not seeing them so of cause our "yang" energy will be lesser if we let them come across us hence we will easily get sick or meet accident at night (most serious accident are happen at night)
So today our medical technology is advance it can explain in the scientific way, during night time the environment temperature drop and difference than day time, human antibody also will be affected by the temperature so we will easily attacked by virus, this is more worst when normally night time human like to go place with air-condition with packed of human exp. Cinema, clubs, pubs pasar malam and etc. this give more chances of we get attack by virus from others.
After the whole day time hard work human usually are tired and need a rest but we not rest and hangout night time so our body get weak this is another important fact that we will sick, so normally night time we will hangout at place with food, mamak, restaurant , cafe that we can easily consume over nutrient like fat and sugar after long term sure our health will be affected.
So not enough rest, consume over diet, expose to virus environment with the low temperature are the cause of let us easily get sick. This not yet include the drugs or alcohol effect that we all know can cause the serious accident happen, tired after all day work sleepy as well will cause accident happen.
from this we know how and why the ancient religion explain all today scientific fact, alot of religion practice cannot be really explain but dosen't mean they are fake, just the matter of time to proof it or how to translate it in modern way.