"When I turned off the light to sleep, I felt it starting to itch after a few minutes. I turned on the light and saw a bunch of bedbugs on my pillow," passenger Muhammad Arsalan told the local Norrländska Socialdemokraten newspaper.
Arsalan found his unwelcome bunkmates on Wednesday night while traveling from Älvsbyn in northern Sweden to Gothenburg in the west.
News of the apparent bedbug infestation caused concern for Sweden's national rail operator SJ.
"We obviously have to look into this and clean the train car immediately if the information proves to be true," SJ spokesperson Telma Henriksson told the TT news agency.
However, Jan Jungerstam, a biologist with extermination company Anticimex, explained that the incident wasn't the first time that bedbugs have taken a trip as non-paying passengers on Swedish trains.
"Bedbugs are parasites that live on people. When they are full and satisfied, the crawl back into the places where they live during the day," he told TT.
The bugs happily hitch rides in passenger luggage, which is a common way for the bedbugs to spread.
Jungerstam added that finding bedbugs on a train has nothing to do with a failure to properly clean the train car or poor hygiene. Rather, it's more likely due to an unfortunate coincidence.
"Anyone can end up with bedbugs and have the bad luck of bringing them home. There's absolutely nothing strange about it happening and considering bedbugs are very common insects, it's a big problem for society," he said.