Why men fall asleep after sex and other post-coital mysteries solved

Don't be offended if your partner falls asleep after sex. (Getty Images)
Don't be offended if your partner falls asleep after sex. (Getty Images)

From falling asleep after sex to the sudden urge to cry, all sorts of strange bodily quirks can happen straight after a session and in the days that follow… We asked our experts to explain the reasons why.

Why do men sleep after sex?

“It’s all due to the biochemistry of sex,” says Dr Deborah Lee. “During ejaculation, men release numerous hormones and neurotransmitters in the brain. These include noradrenaline, serotonin, oxytocin, vasopressin nitric oxide and prolactin.

“In studies, high levels of prolactin are associated with loss of libido, decreased sexual arousal and an inability to ejaculate" – which basically signals to the man he needs some recovery time before doing it all again.

Couple embracing in bed (Getty Images)
Hormones released during ejaculation can give men a strong urge to sleep. (Getty Images)

“Oxytocin – which has anti-stress effects and can induce feelings of relaxation – and vasopressin, are often released along with melatonin at night,” adds Dr Lee from Dr Fox Online Pharmacy. “So, after ejaculation, when levels of these are raised, the body thinks it's time for sleep.”

When you add the fact that all that exertion depletes the muscles of energy-producing glycogen, you can see why it’s a cocktail for a really good kip.

Why do I get thrush after sex?

Thrush, or to use its medical term ‘vulvovaginal candidiasis’, is a common yeast infection. Although it’s not actually a sexually transmitted infection, it can be triggered by sex. This is because, sex – either penetrative or oral – changes the natural ecosystem of your lady parts.

“Candida fungus is a normal part of the ecosystem in your vagina. However, if this is disrupted by your partner’s fingers, penis or mouth during sex, it can trigger the multiplying of this fungus which may lead to the yeast infection with symptoms of itchiness and a thick, white discharge,” explains Lee.

“If your partner happens to have a penile yeast infection, then your risk for infection increases.”

Read more: How often do married couples have sex?

It’s worth knowing however that thrush does not just occur after sex and this could even be a coincidence.

“Candida tends to occur in those who have a weakened immune system,” says Lee. “This means it sometimes occurs in women after a course of antibiotics, and is more common in pregnancy.”

Woman in bed holding her stomach
Having sex can change your body's natural ecosystem which in some cases can cause thrush. (Getty Images)

“The first thing to do if you think you have thrush is to get an accurate diagnosis. Although thrush is a common condition, the majority of women who think they have thrush because something feels wrong down below – don’t have it – they have something else, for example, bacterial vaginosis (BV).” More on this later…

“If a woman thinks she's 'got thrush again', it’s always vital to get this checked out,” Lee emphasises. “If it is recurrent, you can be given regular antifungals to keep this under control.”

“It’s also worth noting that chemical irritation of the vulvovaginal tissues is common too. This could be due to an allergy to certain hygiene products, lubricants or latex.”

Why does my vagina smell after sex?

Firstly, there are plenty of normal smells after having sex that you don’t need to worry about. A healthy vagina has its own smell that is entirely unique to you. Plus, normal semen has a bleachy, chlorine-type smell and, if you’re using a condom (and you should), or lube or sex toys, they’re going to bring with them specific scents too.

Read more: 7 sex hygiene habits you really shouldn't skip

If you notice an unpleasant smell after sex, however, it could be a sign of the infection bacterial vaginosis (BV).

“This is a very common condition in which the balance of normal bacteria in the vagina has been disturbed,” says Lee, by basically a penis entering you or saliva from someone’s mouth on your skin.

“Many women are unaware they have BV,” says Lee. “In fact, as many as 60% of women who think they have thrush, in fact, have BV.”

“It often causes a thick discharge with a fishy smell. After sex, because sperm is alkaline (between 7.2 and 7.8 pH) and a woman’s healthy vagina is acidic (3.5-4.5 pH), it tends to worsen symptoms of bacterial vaginosis, including the discharge and the smell.”

“Rarely, a fishy smell can indicate a trichomonas infection. STIs such as gonorrhoea and chlamydia can also cause an unpleasant-smelling vaginal discharge, although a smell is a less common feature,” says Lee.

Always see a doctor about any smell you are worried about.

Why do I feel like crying after sex?

Often find yourself having, or wanting to have a good blub after sex? Don’t worry, it’s probably just those hormones again, as Lee explains: “Just like men, women release a whole cocktail of chemicals during sex and orgasm. Oxytocin and dopamine make us feel warm, loved and relaxed. Sometimes the tears are happy tears – we often cry when we feel emotional, and this is no different.”

Woman crying in bed
Some women may feel like crying after sex – it could be down to a surge of hormones or they could even be 'happy tears'. (Getty Images)

“However, some women get the postcoital blues which is sometimes called postcoital dysphoria. In one study 46% of men and women had experienced this at least once during their lifetime,” Lee continues.

“Postcoital dysphoria probably has many underlying causes which stem from relationship issues, feelings of guilt or shame or even personal trauma, for example, sexual assault or abuse. If you think postcoital dysphoria is troubling you, it’s time to see a psychosexual therapist.”

Why do I get cystitis after sex?

“Some women are prone to UTIs and often find they occur after sex,” says Lee. “This is because there are huge numbers of bacteria living in and around the vagina and the urethral opening (the opening of the bladder where you pee from). The friction of sexual intercourse can mean bacteria get inside the urethra and from there, they are able to reproduce and get up inside the bladder.”

“Peeing immediately after sex is one way of reducing the risk of a urinary tract infection (cystitis) because it removes the bacteria from the urethra.”

Why do I get cramps after sex?

Woman in underwear clutching stomach in pain (Getty Images)
There's a surprising reason why you may suffer stomach cramps after sex. (Getty Images)

Find yourself cramping up after sex? It may just be the small price you have to pay for a terrific orgasm! And nothing to worry about.

“Orgasm causes your pelvic muscles to contract which can cause discomfort,” says Lee.

“Also, prostaglandins – hormone-like substances in sperm can cause uterine contractions.”

Read more: How does sex affect your period?

Why do I bleed after sex?

There are many potential reasons why you bleed after sex and occasional, light bleeding is probably nothing to worry about.

However, “Sometimes, bleeding after sex (post-coital bleeding or PCB) could indicate a problem,” says Dr Verity Biggs, women’s health specialist at H3H, “such as cervical ectropion (a benign condition of the cervix), pelvic inflammatory disease (PID), polyps, a cervical infection, or, in rare cases, gynaecological cancers such as ovarian and cervical cancer.”

“Bleeding after sex could also be due to damage to the vagina such as little tears. During perimenopause, falling oestrogen levels cause vaginal dryness which can sometimes cause friction and resulting bleeding.”

Up to 9% of women have post coital bleeding, according to research, so it is common. If this happens, you should always report it to your GP or go to the Sexual Health clinic.