Emotions: a harmless vibration?

I am learning that we usually try to avoid negative emotions (by buffering or others actions or inactions) and that doing so is not useful or necessary because our emotions are just vibrations that cannot harm us and that we just need to recognise, welcome and process them.
I do not understand when we say “harmless” as emotions can dramatically impact our health, even make us sick.
Becauses sometimes I am scared and yes, I am trying to avoid to feel a certain way because I am also afraid that if I welcome my emotions if I let them be, they might hurt me even more by weakening my immune system.
So how do I need to understand this? In which way?