Is hiding your emotions unhealthy ?

Yes and no. It depends entirely upon the situation and who you're with. Hiding emotions is part of human nature. It's not wrong to do so. However, it's best if you have outlets to vent the pent up feelings every once in a while. It can be a friend, a stranger, or just a willing pillow. Letting it out every once in a while is important. Else, you might blow like a volcano from all the pressure building up inside.

Of course it is. But we don't always like to share, even if we know we need to get it out of our system. I'm only human. And hiding my emotions is what I do best.

Hiding your emotions mostly is not a healthy habit, these are emotions that make us special and loveable and different from Machines. If you hide emotions rarely is fine, however, it is good to avoid hiding them at all times. If we keep on hiding them it will become a problem in the longer run, people when hiding the emotions are likely to become extra sensitive and can have quick mood swings. When we do not express the emotions, we also create gaps in the relationships. As an expression of emotion creates live in the relationship. Emotional are the one which are truly felt by heart.

It can be! In certain circumstances, it can be understood. Like not wanting to show your jealousy towards someone because you genuinely want to be happy for them but feel "weird" because of your shortcomings. Some might do this for culture, societal, ect reasons. It's normal to feel certain ways and expressing your emotions is important. I'd say people hid emotions because they feel bad about it and don't want it to rub off on someone else. But the best thing you can do is communicate it and what you'd like to feel. Investing in learning how to process your emotions will be worthwhile.