Meditation and Breath

Hi, I have started meditating every night before I go to sleep. Now in just 2 weeks I went from 15 minutes to 40 minutes and eager to continue. While meditating when I reach quite phase no sensation of my body no thoughts, I also don’t feel my breath or very low breathing. At that moment I don’t feel comfortable with that phase as I get anxious to get out of that state and reach for regular breathing. I try to get myself out of meditation. My anxiety does not let me enjoy that moment. How do I handle that?. It is my main cause of anxiety. I am Vata type and feeling fatigue. When I try to do any kind of exercise or any fast movement I get anxiety since I am scared of my breathing pattern. Please help me here as I am waiting for a breakthrough of this pattern. As per doctors I need to do exercise. I have started to go for a walk 15 minutes in the morning. Your help is appreciated.