[sto_hristo]

That is normal. Even one of the best recent Presidents can "struggle" with interviews. See: https://www.youtube.com/watch?v=V4bDuFJuriw This is the best speaker on the planet. On the planet. His bread and butter is pro-speaking actually. "Struggle" in quotes, because he's not struggling really, it's just how normal human beings speak as they are constructing answers in their brains.

But why on most of his others interviews he was going so smoothly and effortlessly? Because those were scripted and everything was predictable and prepared for in advance by a huge staff in the background. He already has all the answers in the brain and is merely giving a mental reading.

So ground yourself. You're not giving speeches and your interview is NOT going by a script you've been given prior. Relax, answer questions to the best of your ability and KNOW THAT you'll be judged most likely by people with skills inferior to yours.

Looking at other answers asking you to prepare for interview as if you're running for president. Sure thing. Do that. But only if you're actually running for president and there are millions on the table for the taking.