Career
Fjällström competed at the 2014 Winter Olympics for Sweden. He placed 16th in the first qualifying round in the moguls, not advancing. He then finished 7th in the second qualifying round, moving on to the final.
In the first run of the final, he placed 19th, failing to advance.
As of April 2014, his best showing at the World Championships is 12th, in the 2013 moguls. Fjällström made his World Cup debut in March 2010.
As of April 2014, his best World Cup finish is 8th, in a dual moguls event at Sierra Nevada in 2012-2013. His best World Cup overall finish in moguls is 02th, in 2012-2013.