My family has been practicing Twin Hearts meditation by Master Choa Kok Sui (of Pranic Healing) for about an year. It is a guided meditation where a star or light is imagined simultaneously at the heart and at the top of the head and golden light is imagined flowing to the body through the head into the heart and to the hands - and is eventually directed to an imagined globe with blessing intent.
After reading Yogani's writings I always wondered whether this is a safe practice, and whether it would lead to premature crown opening. Recently, my mother-in-law who has been practicing this meditation complains about constant burning sensation in the head, feeling of a bulge at the crown and heaviness and headache. Could this be over activation of crown chakra? I wonder if anyone here could comment on Twin Hearts meditation and potential premature activation of crown chakra.
The simple answer is yes. The symptoms your mother-in-law is experiencing are classic symptoms of a prematurely awakened crown chakra. It would be wise for her to stop the practice and to get advice from someone who is experienced with the awakening of kundalini and the purification of the subtle body.
In general, practices which involve sustained attention, or visualization at the crown chakra are not safe for beginner practitioners, and often not even for advanced practitioners.
For more details see lesson 198 and 199 and also lesson 287.