Fatigue-Unable to sleep because of erection.
Lower back pain-Poor posture due to hiding erection in inappropriate situations; eg. Beloved Aunt Martha's funeral.
Stress/Anxiety-Causes are many, but amongst the foremost is wondering if, without relief, erection will explode.
Thinning hair/Hair loss-Incorrect. Merely a transference from the head to the palms.
Soft/Weak Erection-Caused by trying to do it immediately again. Wait a few minutes.
Premature Ejaculation- It's masturbation, who cares!
Eyefloaters or fuzzy vision-Do NOT ejaculate upwards towards your face (may apply only to those with Peter North syndrome).
Groin/Testicular pain-Blue Balls is worse.
Pain or cramping in the pelvic cavity and/or tailbone-Occasionally lie to one side or the other, rather than on the back, when doing it.