Most men have an off-day sexually at some time in their lives. Erectile dysfunction can be due to lifestyle factors - a stressful job, recreational drugs, too much alcohol or not enough sleep.
It also increases with age but you don't have to suffer in silence. Reduce stress with exercise, try therapies such as reflexology or meditation and cut down alcohol consumption.
For women also, life can interfere with libido.
Bringing up children - who feels sexy when they're surrounded by screaming kids? - trying to balance work and home commitments, not to mention physical influences from menstruation to pregnancy to menopause all affect sex drive one way or another.
Herbs to help
Herbs to help include oats, horny goat weed funnily enough, saw palmetto, damiana, the African root yohimbe, ginkgo biloba (promotes circulation and blood flow), maca from Peru, tribulus terrestris (for low sex drive), the amino acid I-arginine, pulsatilla, motherwort and ginseng (an adaptogen) that boosts energy and improves libido.
Supplement
Low sex drive can be explained by low testosterone levels so increased B vitamins should help here while supplementing with zinc can help prevent impotence in men and protect fertility in men and women.