Giddy: really excited about something to the point of being giggly or silly. "She was giddy with excitement"- When you are so excited about something that you can't contain the excitement. Dizzy: When you feel like you are going to faint. You could say "dizzy with excitement" but that isn't used as commonly.

Dizzy is a synonym of giddy. And It means having a sensation of whirling, with a tendency to fall EX; They climbed to a giddy height. EX; I stood up too fast and felt dizzy .