You can, however, reclined or semi-reclined positions are known to impair respiratory muscle function.
This is why we recommend sitting upright in order to practice proper diaphragmatic breathing during training. If you’re having trouble maintaining proper breathing while sitting upright, try leaning back a little during training. You may find this easier to complete your training properly in the beginning.
However, as soon as possible, sit in an upright position since inspiratory muscle function is optimized while sitting or standing.