Patients will either sit or stand while wearing a head mounted display (HMD, Oculus Rift). A 360° video, showing a neutral body from the back in a neutral room, will be projected onto the HMD.

We will record the patients' ECG throughout the entire experiment. Raw data (ECG) are acquired with Arduino and in-house software will detect, in real time, the peak of each R-wave from the recorded ECG data and trigger an additional visual stimulus (e.g. a flashing outline surrounding the virtual body) that flashes on and off ASYNCHRONOUSLY with respect to the participant's heartbeat. The silhouette surrounding the virtual body flashes for a duration of 100ms and with a sinusoidal opacity.

Standard multimodal out-patient therapy program (psychological support, physiotherapy, ergotherapy).

Explore the analgesic effect of the cardio-visual illusion in patients suffering from chronic pain as compared to a VR control condition using algometry:

The Pain pressure detection threshold to determine hypersensitivity to pain is measured with a standard electronic algometer (Somedic Type II) by bilateral testing on the middle fingers. The electronic algometer is calibrated following the standard protocol as recommended by the manufacturer and set to deliver a steadily increasing pressure (50 kilopascal for 1 s). In this method, the investigators check for the threshold at which non-painful perception of pressure changes to painful perception in response to the gradually increased pressure applied. Low thresholds correspond to high pain sensitivity.

Explore the analgesic effect of the cardio-visual illusion in patients suffering from chronic pain as compared to a VR control condition using algopeg:

The algometric measurement method to detect hyperalgesia will be carried out by means of a pressure pain provocation test. For this type of algometry, we will use a standardized peg with a clamping force of exactly 10 Newton at an extension of 5 mm (Type Algopeg).The pressure is applied on the middle finger and the ear lobes for 10 s each and is invariable. The pegs pressure exerted on an ear lobe is perceived as being consistently and clearly above the pain threshold. The patient indicates the pain intensity on a numerical rating scale (NRS) on which 0 stands for "no pain" and 10 stands for "the most intense pain imaginable". High NRS values correspond with high pain sensitivity/hyperalgesia.

Inter-beat intervals are calculated as the time between two successive R spikes using the ECG signals as acquired during CV stimulation. Raw data are processed in Matlab® (The MathWorks Inc., Natick, USA) with the HRV Analysis Software (HRVAS: HRV Analysis Software). For each subject and each condition, we calculate the square root of the mean squared differences of successive beats intervals (RMSSD), which estimates the short term components of HRV and is commonly used over short recording periods. As HRV pain-related changes occurs mainly in high frequencies (i.e. power spectrum between 0.15 to 0.40 Hz), we then compute frequency-domain HRV analysis and calculated the power spectrum density using Welch's methods for Fast-Fourier Transform.

Study the reduction of psychological distress measured through the Hamilton anxiety and depression scale (Score Anxiety 0-7 normal, 8-10 borderline, 11-21 abnormal; Score depression 0-7 normal, 8-10 borderline, 11-21 abnormal)

Study the reduction of psychological distress measured through the Beck depression inventory. BDI-II contains 21 questions, each answer being scored on a scale value of 0 to 3. Higher total scores indicate more severe depressive symptoms. The standardized cutoffs used are: 0-13: minimal depression; 14-19: mild depression; 20-28: moderate depression; 29-63: severe depression.

Study well-being through the WHO 5 Well Being Index.

The WHO-5 consists of five statements, which respondents rate according to the scale below (in relation to the past two weeks).

All of the time = 5, At no time = 0.

The total raw score, ranging from 0 to 25, is multiplied by 4 to give the final score, with 0 representing the worst imaginable well-being and 100 representing the best imaginable well-being.

Explore the analgesic effect of the cardio-visual illusion in patients suffering from chronic pain as compared to a VR control condition using the numeric rating scale (0-10; 0=no pain, 10= max. pain).

Explore the analgesic effect of the cardio-visual illusion in patients suffering from chronic pain as compared to a VR control condition using algometry:

The Pain pressure detection threshold to determine hypersensitivity to pain is measured with a standard electronic algometer (Somedic Type II) by bilateral testing on the middle fingers. The electronic algometer is calibrated following the standard protocol as recommended by the manufacturer and set to deliver a steadily increasing pressure (50 kilopascal for 1 s). In this method, the investigators check for the threshold at which non-painful perception of pressure changes to painful perception in response to the gradually increased pressure applied. Low thresholds correspond to high pain sensitivity.

Explore the analgesic effect of the cardio-visual illusion in patients suffering from chronic pain as compared to a VR control condition using algopeg. The algometric measurement method to detect hyperalgesia will be carried out by means of a pressure pain provocation test. For this type of algometry, we will use a standardized peg with a clamping force of exactly 10 Newton at an extension of 5 mm (Type Algopeg).The pressure is applied on the middle finger and the ear lobes for 10 s each and is invariable. The pegs pressure exerted on an ear lobe is perceived as being consistently and clearly above the pain threshold. The patient indicates the pain intensity on a numerical rating scale (NRS) on which 0 stands for "no pain" and 10 stands for "the most intense pain imaginable". High NRS values correspond with high pain sensitivity/hyperalgesia.