It is not uncommon for men to experience an erection during a massage, especially if the massage is being given in the genital or prostate area. Erections can occur for a variety of reasons, including physical stimulation or simply due to the relaxation and comfort of the massage.
If you experience an erection during a massage, it is important to remember that it is a normal and natural bodily response, and it is not a cause for embarrassment. Your massage therapist is a professional and has likely encountered this situation many times before. It is their job to ensure that you are comfortable and relaxed during the massage, and they will not be offended or distressed by an erection.
If you are still concerned about the possibility of an erection, you can always let your massage therapist know beforehand and discuss any concerns you may have. They can take steps to make you more comfortable during the massage, such as draping a sheet over the area being massaged or avoiding certain techniques that may be more likely to cause an erection.