Hair growing in a dream usually reflects returning vitality -- energy, confidence, or self-expression coming back after a period where it felt diminished. Thick, fast-growing hair can point to a renewed sense of identity, a visible sign that something in you is regenerating rather than fading away.
He that has too great a conceit of himself will be apt to fall into many errors in his judgement; yet on the other side, he that is too diffident, is not fit for this Science. - Cardan Girolamo (1501-1576)