I was able to do them earlier fine. I started with holding my breath at 5, then bumped up to 8, 10, then I can hold my breath for 12 seconds without straining. I was able to do it with 12 second hold without pain either. Actually I feel more accustomed to 12 seconds. Anyways today I did it (A little late but under 24 hours) and I felt sharp pain in my chest after the 8th one. I stopped immediately of-course but its pain lingers on even now as i right. Should I change the exercise or lower my holding seconds? This pain isn't unbearable but its sharp. I take that back, I tried to lay down after writing this and its pain only continues.