@Allkpop posted an update as to why the concert was cancelled and here it is. BTS has cancelled their Japanese show 'HwaYangYeonHwa on Stage' in Kobe. According to Big Hit Entertainment, Suga and V experienced nausea during rehearsals, and were rushed to the hospital for a checkup. CT scans showed that there wasn't anything wrong with them, but that it was nausea due to heavy movement during their concerts. Big Hit Entertainment decided fans should not see an incomplete BTS on stage and have decided to cancel the two shows altogether. The statement read, "We are making this announcement because the '2015 BTS LIVE HwaYangYeonHwa on stage ~Japan Edition~ in Kobe's World Hall on the 27th and 29th will be cancelled. Before the concert, Suga and V experienced nausea, so rehearsal was cancelled and the two were rushed to a nearby hospital for professional medical diagnosis. The CT scans showed no big concerns, but the two were diagnosed with nausea possibly due to large movement during concerts, and that they should be kept under watch. The two members strongly wanted to stand on stage to meet fans who came to see them, but are currently resting under strong recommendation by the medical staff, and thankfully are recovering quickly. However, we decided that we cannot show a lacking stage with a concert without all the members, so we have decided to cancel all schedules around the Kobe concert, including today's. The members will be quickly returning to Korea so Suga and V can have a detailed checkup. We ask for the understanding of all the fans who came to see the boys. We will minimize loss by completely refunding the tickets to both concerts. We sincerely apologize to the audience as well as all the fans. Once again, we are sorry to cause concern. Get well soon, Suga and V!"
Credit goes to @Allkpop
I am really happy that it's nothing serious but it honestly still scares me. Get well soon V & Suga!
There's update on the boys. Click here