This is from DailyMail UK:
In fact, Professor Ian Macdonald, professor of metabolic physiology at the School of Biomedical Sciences in Derbyshire, warns breathing too deeply can do more harm than good.
‘Inhaling and exhaling too deeply can disturb the balance between carbon dioxide and oxygen in the body needed to neutralise the blood. This can cause light headedness and even make someone faint.’
Complete article at: http://www.dailymail.co.uk/health/article-54709/Can-really-lose-weight-breathing.html#ixzz2TzzMe9vX