Rather than calling it as a downfall we can call it as a major correction in Dia's price. It was quite expected since the coin increased a lot in price in a short span of time. It's not only with Dia but any coin which increases in price too soon has to fall back a little in order to give an opportunity to other investors to join in. It has also happened with bitcoin when the price increased to $20k and then dumped to $3k.
Corrections are expected in crypto. There's nothing to worry about since the price will increase again in future.