I've had this happen and have always been told it's "stress". Although it seems that stress is used for an explanation to a lot of things, often it really is the cause. Fight or flight (adrenaline) causes the digestive system to slow down or even turn off. Stress due to new situations (even if you don't think it should be a big deal, your subconscious does) is often like an adrenaline rush in that our body redirects so to speak energy from the systems that are not needed at the time.
I hope this helps a bit.
You say you feel normal and don't feel bad, so it's obviously not fight or flight -- you'd know if it was that! It's also not true that fight or flight -- basically and anxiety attack -- causes lack of hunger -- it can just as easily cause too much hunger, as eating is a good way to avoid. But the poster doesn't sound anxious. I'd say you're just not hungry.