Shortness of breath while water fasting

Helo fellow fasters,
I m on day 14 of a waterfast and things are going very well. The only thing that bothers me a little is that I have shortness of breath. It takes me a lot of efforts to take deep breaths,and seems like something heavy is on my chest, or like my lungs can t expend anymore. I have water fasted many times before but that never happened.
Has anyone ever experienced shortness of breath during a fast?
And does anybody have an idea as to why it could happen? I tried to find an explanation but coudn t find any. It s just out of curiosity because I trust my body while fasting and know everything is for the best.
Anyway,
Thank you in advance!
Eska