Breath techniques

How long does it take for those sensations to arise?

Almost instant. However, just before writing this comment I tried Ham-Sah pranayama while lying in the bed. This time I do not feel that bad but still there is small headache.

I also searched these sensations on the internet from various yoga etc. sources. I read about others having similar experiences. And some said It may be related to the fact I breathe in a lot more than breathe out. But I am not sure if it is related to breathing only, since I felt similar effects when I did only imagination of the energy moving to upwards.

I am 21 years old, and these practices really help drying out my semen. And when I do not do any transmutation practice for a long time, I feel similar "things" you mentioned about middle age monks and that bothers me really a lot. I have a "strong" will. Maybe, I might also mention that I follow Muslim practices, regular prayers etc.

Many people feel discomfort when first starting to us these exercises. This is because the pathways are very dirty, and as the exercises clean them, things get "stirred up." This is similar to what happens when you first start physical exercise: you can feel nausea, dizziness, etc, because the blood was stagnant. Once you get used to it, those negative sensations go away. For most people, this happens quickly with regular practice.

Thanks, is there any other things that I should consider such as doing the exercise with empty stomach, in early morning etc. ?

The two most important details are:

Relax thoroughly before and throughout the exercise

Pay attention to what you are doing. Do not become distracted.

I have another questions about Ham-Sah pranayama. While doing ham-sah pranayama, is the mantra important? I recite some Islamic dhikr while inhaling and exhaling. Also should I hold the breath for some time between inhale and exhale? Or exhale immediately after inhale? Thank you so much.