Celsius is down 35% in the last month. Here are four reasons why it's time to buy the upstart energy drink company.By disrupting the energy drink duopoly owned by Red Bull and Monster, functional energy drink upstart Celsius (CELH 8.32%) has grown to account for 11.5% of its industry's U.S. sales -- becoming the only new brand to reach this mark in the last decade. Now firmly the No. 3 brand in the energy drink space, Celsius is larger than the No. 4 and No. 5 labels combined. It's grown from a mere 3.5% sh ...