Answer may be:

If you are a beginner in Yoga, pushing too hard can cause your blood pressure to drop and feel dehydrated. This can make you feel dizzy so keep yourself hydrated and go slow.

Sometimes you might feel dizzy while deep breathing because you are exhaling carbon-di-oxide faster than the body is producing which causes chemical alteration in your body and makes you feel dizzy. The best thing to do is breathe slowly and less deeply.

Dizziness can also come if you stand up suddenly from Uttanasan, this causes a sudden blood rush to flow down to the legs and abdomen and too little blood fills the heart. This is compensated by a natural reflex system of the body.

So let your body come back to the normal state and then start with the next asana.