Yes, you have successfully made contact. What youve described about the sigil is called “flashing”, it happens when sigil has been charged with energy and contact with the spirit has been made.
Physical sensations are also attributed to the energy of the working and nature of the spirit you are contacting. These range from various emotional to physical reactions and what you get depends on the spirit in question. For example, when calling upon Lilith its not unusual for me to feel the taste of blood in my mouth, since she is of vampiric nature, or when calling upon Lucifer, I feel a soothing sense of tranquility.
Now, about brain fogging up, when doing these rituals you enter a certain state of mind. In this state rational mind takes a back seat and intuition takes over. Thats what you want for rituals to be easy and successful, dont worry about messing up the enns and dont think about too much about rigidity of the ritual, do what feels right at the moment. Ritual is not about following it step by step to a tee, its about immersing yourself in it and making it your own. Also, just so you know, spirits are not as pedantic as you think.
Btw, keep Lucifer in mind, he might be able to help you in other areas of your life.