After allocation has been completed, patients in the intervention group will receive a pair of numbered wooden prisms with dimensions 20x18x18 cm along with written instructions about the correct use of the intervention. The patient must sleep with HBE during 6 weeks and both RDQ and SF-36 questionnaires will be applied again at the end of this first period while the participant is still sleeping with HBE. Afterwards, a washout 2 week period follows in which the participant sleeping with HBE will stop using it and will return the pair of wooden prisms to the researchers. After washout period has ended and both RDQ and SF-36 questionnaires have been applied again, patients allocated to the control group during the first period of the study will receive a random pair of prisms and will be instructed to use the prisms for sleeping with HBE during a second period of 6 weeks. Meanwhile, participants initially allocated to the HBE group will be followed as a control group in this second period of the study.