The idea of Bramh put forward in the Upanishads is not one which can satisfy the demands of the mind.
The 'knowing' of which the Upanishads speaks is of a different order.
Hinduism is without doubt the most monotheistic religion in the world because it recognized that the Supreme can only be diverse and that he incarnates Himself in many forms - hence the millions of gods in the Hindu pantheon.
Remember to breathe and always start your yoga practice with a brief meditation.
Hinduism is often labeled as a religion of 330 million gods.
When there is nothing for the mind to attach itself to, it will slip away from meditation or will glide into a state of slumber.
Therefore the wise will meditate on some form, remembering, however, that the form is a superimposition and not a reality." Its traditions extend back long before recorded history.