It is kundalini energies, and represents increased spiritual awareness. Kundalini energies do not always work in the way people say they do, they can start at the crown, just as much as they can start at the root, and they can be spontaneous like anything else, do to our natural spiritual growth and awareness they will be wherever we are increased in naturally, they can be opened by increased awareness in any area, and in all, it signifies a great turning point for you, such as if the sensations start at your crown, i can highly bet, they will begin to move downwards sometime, maybe soon. It may be backwards, but it is highly more revered than the opposite, since it starts at the crown, you already have much experience of spiritual awareness and contact with the higher source, the only downside is, it probably means your lower chakras may be less grounded because of such. If the serpent is awakened in you, those energies will shoot like lightening bolts, down your spine, to make it known in your other chakras anyway, and you will still have the constant tingling in your crown. Personally, i always have the constant sensations in my crown, along my face too - that is said to be a highly good sign. Kundalini energies shooting downwards, and up, are good to ground the other chakras from your always working crown chakra.
Kundalini rises, and kundalini falls. And after that, kundalini rises, and kundalini falls. Kundalini does many spontaneous things between that all.

It is correct, the main point all wish to get to, is the crown, but for some people such as you, and such as I, and such as many, the kundalini starts there, which would be due to the fact you are already sensitive and open in that area of spiritual consciousness, or simply, more so than other areas. Mainly, it happens in the root for most people, because they are more earthy creatures. The life force, itself stems from the root, but in some cases, that life energy naturally rises to the crown in people who are more expanded, so naturally they do not feel it, and there it starts.

This is a greater endeavour than pulling prana from the feet, in fact many gurus believed achieving kundalini to be better this way, and it is more rare, to have the life force energy prana, to be pulled in from the crown firstly. It can unground you much though, take it from my experience hehe. It means your lower chakras have already released, and the energies are starting from the top.

For some people, when kundalini energies "seem" to start at upper chakras, they can tend to lose grip of it, which can mean various things, like imbalances, or blockages that do not allow the energy to move downwards, or just not fully in the time to be awakened yet, this can explain those who manage to "open" the third eye, or "stimulate" the crown by force or just by being overly spiritually connected, yet the prana is not yet ready to be awakened fully.