Stop. Fasting should not make you lightheaded or dizzy - especially at under 24 hours. You should feel better when you fast than when you’re eating (if a little hungry sometimes).
Stop and try intermittent fasting first. And learn about fasting before you jump into it again.
In my opinion, if you’re feeling dizzy or lightheaded, break your fast. Your body is telling you something is wrong. Most likely, since you’re new to fasting, it’s telling you that it’s run out of glucose and glycogen stores, but can’t metabolize fat fast enough to supply all the energy you need. i.e., you’re not yet metabolically flexible, AKA “fat adapted”
Do some research about metabolic flexibility, and start with intermittent fasting. 18/6 should be safe and easy for the average person that doesn’t take any meds that need to be taken with food. Once that’s comfortable, gradually shorten the eating window. Eventually you’ll become metabolically flexible and can fast for longer periods (keeping in mind you’ll also need electrolyte supplements for extended fasts).