Objective Measurement of Pain Regulation in Individuals Who Have Received Internet-delivered Exposure-based Cognitive Behavior Therapy

Inclusion Criteria: * ≥18 years of age * Diagnosed with fibromyalgia (indicated by a diagnosis from a physician and confirmed by the Fibromyalgia Survey Questionnaire during the assessment interview) * Access to the internet * Willing to refrain from other psychological treatment during the study, * Registered with Swedish personal ID number and residing in Sweden or Finland * If taking antidepressant or antiepileptic medication, this must be stable for 4 weeks prior to baseline measurement, * Willing to come to Karolinska Institutet and participate in pain tests on 3-4 occasions, and * Gives informed consent Exclusion Criteria: * Treatment-requiring depressive- or anxiety disorder, eating disorder or stress-related ill health, indicated by a score of ≥35 on the Montgomery-Åsberg Depression Rating Scale-Self-Rated (MADRS-S) and confirmed in a clinical assessment interview as severe depression; ongoing diagnosis of PTSD or exhaustion syndrome, unstable or unmedicated bipolar syndrome, severe obsessive-compulsive disorder or eating disorder * Active suicidality, indicated by ≥4 on item 9 of the MADRS-S and confirmed in a clinical assessment interview * Psychotic illness * Late pregnancy (≥29 weeks at treatment start) * Other somatic conditions requiring immediate treatment and/or assessed as the participant's primary problem, including other dominant pain problems and chronic fatigue syndrome (ME/CFS) * Ongoing alcohol or substance abuse * Opioid use * Insufficient knowledge of Swedish or computer use to benefit from text-based treatment.