That depends on your definition of "insanely heavy".........yeah, they definitely get heavier as they grow, but it's a slow process.....like the person above said, your neck muscles usually adjust with it.....although some people do have problems with weight and have to cut because of it.....that isn't common though.
my hair is so fine and straight it would not lock up on its own........ I am not shitting you!! I can wash it and it looks like it is getting knotty... then when it dries... poof, all gone we had to backcomb a bit and palm roll my hair to get it to dread.......... we palm rolled them on a pretty regular basis.................. actually did em a lot of good and kept em all nice and round (if your not into round uniform looking dreads and want crazy fuckers, palm rolling probably isnt for you)