Playing a musical instrument is physically demanding work for which you need plenty of oxygen. Many people have a tendency to hold their breath while playing, especially during difficult passages. This makes your playing less relaxed, your shoulders may tense up, and you may feel unwell due to lack of oxygen.
You should examine your breathing while practicing. Unrestricted breathing furthers relaxed, natural playing.
Phrasing is musical breathing. Sometimes you may feel as if intensive phrasing requires you to hold your breath. This is, however, different to a compulsive holding of your breath during difficult passages.