The Hammers are at another of Zola's former clubs, Chelsea, today.
Zola told The Sun: "I could have started my management career with an easier situation.
"In my two years I had to handle situations that some managers don't deal with during their whole careers. So many people have come up to me to say how they felt for me.
"They were saying my face just wasn't the same. I'd stopped smiling, I looked tense, and seemed to have aged overnight. That's not like me. I love to smile, to enjoy my life and enjoy my football.
"I played the game until I was 39 and I can honestly say that it never ever felt like a job to me, it was always a joy, a pleasure.
"But when the pressure was on I let it show. I also brought it home with me. You are supposed to leave your work behind at the office - but I didn't do that.
"I found it hard to switch off and took it all home.
"Maybe the players sensed that I was nervous, that I was worried. Maybe they could smell it. So that's a big lesson and I will never make the same mistake again."