*) Is there a top-down kundalini? (which could start from the crown and gets down the body)
*) Can there be a kundalini awakening without the person knowing it?
*) I could feel energy activation continuously on my forehead — Any suggestions on how to handle it?
*) During meditation I had a warmth on the back of my head and could see a small thing (Pineal gland?) which was on my back of my head- then I had a huge brain massage for quite some — Any thing to take care here?
I will answer your questions according to my understanding and experience of the inner pathway to liberation. Swami Kriyananda has given excellent descriptions of the inner spinal centers and energy pathways in Lessons 12 and 13 of the Raja Yoga Course of Self Realization and I highly recommend you read these.
To answer your first question — no there is not a top down kundalini power. There is the energy of the descending pingala current in the spine upon exhalation.
I suspect there can be a kundalini awakening without a person knowing it depending on whether or not one has awareness of the inner currents in the astral spine.
Energy activation in the forehead is probably a sensation of energy in the positive pole of the 6th chakra, spiritual eye or Christ center. You would feel this center at the point between the eyebrows. It is helpful to focus your attention on the spiritual eye as often as possible to uplift your consciousness especially in meditation and throughout your day as well.
Regarding your last question, I suggest you tune in to whether or not the experience you had was spiritually awakening, sidetracking or simply energy in the head. By spiritually awakening, you would have felt peaceful, joyful and uplifted. Sidetracking would have been a diversion of attention towards phenomena rather than significant spiritual awareness. Energy in the head can be warm or cool and may or may not have much to do with meditation. It can result simply from concentration. During meditation, keep your awareness at the point between the eyebrows and penetrate any light you see there with calm and relaxed attention.
Again for a more complete description of the kundalini energy and the ida and pingala currents in the spine I refer you to Steps 12 and 13 in the Raja Yoga Course book.
Joy to you!