Dear Thygarajan Sir, I am not equipped to find the reasons for such experiences. It is true some of those experiences are fearful and that is why my last sentence mentioned about disappearance of mysterious fear in those experiences. Most importantly, I feel high level of energy after meditation session as if I am a newly charged phone. I remain fully in thought mode 10 minutes into meditation but only after that I lose thoughts about breath and the sound of inhalation and exhalation. Earlier, I used to lose track of time but now I am able to get back with deep sense of intentional break into meditative sessions. Only once, I felt that I was gasping for breath as though I have forgotten to breath going inside. Only that fear stopped me from meditation. It confirmed fear of death is deep inside me. But inside journey is remarkable and similar to psychedelic and hallucinative experiences. Like you I also wonder what are those geometric patterns. My wishful mind tells me that those are my Vasanas (encryption) and if I could find a code to crack that, I will end the cycle of birth and death. I will never know what they mean. Macabre experience could be a valley on top of a peak where you are desireless, detached and full of equanimity. I call them neon signs on the highway diverting us towards the exit from the highway journey towards our destination. Sometimes, I feel those experiences are like suffering from lack of oxygen when we attempt to circumambulate Mount Kailash. Breathlessness gets priority over Lord Shiva in such situations. Note: 4+1+4 is a wrong calcuation as I consider the retention as 1 instead of 4. Frankly, inhalation, retention and exhalation all together is 15 seconds for each cycle.