Why do I feel dizzy and weak after starting HIIT workouts?

I recently started doing HIIT workouts at home after being inactive for almost a year. I usually exercise in the morning on an empty stomach because I heard it helps burn more fat. But after 10–15 minutes, I start feeling dizzy, shaky, and weak. A few days ago I even had to lie down after finishing. Am I doing something wrong or is this normal for beginners?