Giraffes (Giraffa camelopardalis) have long been admired and caused confusion for many due to their long slender necks. The ancestors to giraffes, however, did not have elongated necks (Williams, 2016), leading to early researchers to speculate on how long necks formed in modern giraffe. One such speculation was that individual giraffes stretched their necks and over generations this led to long necks. This is now thoroughly discredited, natural selection does not work this way! Over time, offspring with longer necks were able to survive where shorter neck individuals could not leaving longer neck individuals to survive (Smaldino & McElreath, 2016). It is now thought that longer necks allowed giraffe to reach fruits high in the trees, as well as see predators from farther away.
But to get to the question, there are many potential problems associated with having a long neck. The increased distance from the heart to the brain provides challenges in supplying oxygen and cooling the brain. In response, giraffes have increased arterial development during growth to meet these cardiovascular demands (O'Brien et al. 2016). Surely with extra blood and oxygen, and increased muscle mass to support their heads, giraffes have no problem with neck aches.