मुखं संयम्य नाडीभ्यामाकृष्य पवनं शनैः।
यथा लगति कण्ठात्तु हृदयावधि सस्वनम् ।।
The name is formed by joining two words - Uch and Jayi, which means to control Prana. therefore, it is called Ujjayi Pranayama.
Hatha Yoga also claims that the gastric fire is increased and diseases like dropsy can also be cured by this Pranayama.
Person should not put and extra pressure.
If you feel sick or tired stop this immediately and do Shavasana.