Alcohol in your system
A common cause of erectile dysfunction. Alcohol is commonly used to 'loosen things up' before sex or on a night out. Problem is, alcohol dilates (widens) your blood vessels. If you manage to get an erection, the alcohol keeps the blood vessels to your penis open, the blood drains out and you're left hanging in limpland.
The effect varies greatly from person to person and depends on how much you drink, but in general if you have problems with erectile dysfunction, don't drink before sex. If you've had a few drinks and think you might be having sex soon, stop drinking asap and start drinking water.
Also change in diet, exercise, prescriptions & otc drugs, vitamins can change you ability also.
It could also be subconscious, you might be thinking about the alcohol & siking yourself out or I was told that your body changes every 7 yrs (hair, skin, tastes, smells, sight, hearing, performance, etc).
Alcohol use to make me even more horny then already am so I liked it before sex also but now hard liquor gives me a headache right away & cocktails make me tired so I try to have wine or avoid alcohol all together.