When the practice of Thummo is properly done, then the body temperature goes up. In fact, there are experts in this system who are tested by their teachers, by placing wet cotton towels on their backs to dry them, as they sit down and practise the Thummo. And, the larger number of towels a practitioner dries, the higher up he is supposed to be in the hierarchy of Thummo practitioners.
But then, this is not the aim of the yogi who opts for spiritual development or whose mind is fixed on salvation.
Now, the followers of the Sri Vidya discipline of awakening the Kundalini, also worship the ‘Sri Yanthra’–the ‘Sri Chakra’ which is a diagram drawn to symbolise the infinite primordial energy as it permeates and pervades the entire universe. First, they worship the Sri Chakra or the Sri Yanthra externally and then they transfer it, by drawing the image within their minds, to the Anahatha chakra or the heart centre and offer mental worship to the Sri Chakra with the bijaksharas that are to be chanted until the Anahatha chakra activates and from there the Kundalini is led gradually to the Sahasrara chakra–the culmination of their spiritual practice.
However, there is a simple yogic practice by which the Kundalini may be awakened gradually and made to ascend to the Sahasrara chakra. It is better to practise it under instructions, personally from a teacher, but I don’t think there is any harm in giving the basic details of what it is.
“In fact, there are experts in this system who are tested by their teachers, by placing wet cotton towels on their backs to dry them, as they sit down and practise the Thummo.”
It is a yogic technique that includes a little bit of Pranayama and visualisation. The yogi sits preferably in Padmasana or Siddhasana, closes his or her eyes and then visualises the spinal cord as a golden, hollow, reed-thin tube stretching from the bottom of the spine which is the Mooladhara to the crown of the head which is the Sahasrara.
Then, the respective chakras and their symbols are visualised–the Mooladhara at the bottom, the Swadhisthana between the navel and the Mooladhara, the Manipura at the navel, the Anahatha at the centre of the chest, the Vishuddha at the throat, the Brumadhya or the Agya chakra between the eyebrows and, finally, the Sahasrara chakra on the crown of the head.
Then, a tiny dot is visualised at the centre of the Mooladhara chakra, which should be small enough to enter the hollow reed that is visualised as the Sushumna. So, a shining little silvery dot is visualised and then, the yogi takes a deep breath and as he breathes in, he visualises the little silvery dot, dancing itself up through the hollow of the spine which is the Sushumna, the golden reed-like tube, and touching each of the centres starting with the Mooladahara, then the Swadhisthana, then the Manipura, then the Anahatha, then the Vishuddha, then the Brumadhya and lastly, the Sahasrara.
And then, the breath is held inside and, subsequently, the yogi exhales deeply and as the exhalation takes place, the dot is allowed to descend through the golden tube of the Sushumna touching all the centres as before, till it reaches the bottom-most, which is the Mooladhara chakra. Now, as the silvery dot ascends, each center or chakra is visualised as lighting up like a serial bulb. One need not visualise specific colours but just think of the chakras lighting up, one by one, from the Mooladhara to the Sahasrara.