Angels,
"I sometimes get head pressure along with a rushing sound in my ears (sometimes to what appears to be the beat of my heart) during inverted poses "
It is good that you have not gone deeper into the practice, otherwise the problems that may arise can be magnified a thousand times fold. This is why the technology is not something to tamper with, without a proper understanding of all of the aspects that are involved in it. One of the reasons why certain problems as this happens is because there are certain imbalances that are happening in different parts of the nervous system which affects the internal organs. But, at a much subtler level, the prana - the subtle energies of the body, are being imbalanced because one’s practice is not done in such a way that it creates a certain balance in one’s whole system. For that, certain techniques have to be balanced with other techniques to make sure that such imbalances do not happen. Every asana channels the subtle energy in the body in a very particular way, and it is important to understand which asana does what and how each asana channels energy. Some asanas will awaken certain chakras along the spinal cord, some will awaken certain nadis, some will awaken different aspects of prana.