Standing outside during the winter can get cold fast. But just because you are shivering or you can’t feel your toes doesn’t mean you have hypothermia.

Hypothermia occurs when the body loses more warmth than it can generate and its core temperature drops. The National Institute on Aging lists symptoms like confusion or sleepiness, slow and slurred speech, shallow breathing, a weak pulse, arm and leg stiffness, poor motor function and slow reactions as indicative of hypothermia. Scientific American compares the signs to how someone may present when in a “drunken stupor,” and adds low blood pressure and a body temperature lower than 96 degrees Fahrenheit to the mix.

Read: Can We Wake Up Frozen Dead People?

The Centers for Disease Control and Prevention warns that people may not know they have hypothermia. That could be in part because you don’t have to be exposed to subzero temperatures to develop the condition. It can occur at temperatures higher than 40 degrees, for instance, “if a person becomes chilled from rain, sweat, or submersion in cold water.” In addition to hikers and the homeless, the most common victims include elderly people without adequate heating, babies sleeping in cold rooms and people who drink alcohol or use other drugs. Some drugs can interfere with the body’s ability to regulate temperature, like antidepressants, sedatives and narcotics. Hypothermia is also one of the few situations in which being obese is a benefit — fat serves as insulation, keeping heat in the body longer when exposed to cold temperatures.

So what do you do when you suspect you or someone you know has hypothermia? Possibly nothing, if your core body temperature stays above 95 degrees, Scientific American says. “Your body will warm itself up and you generally don't need treatment.” For people with temperatures between 90 and 95 degrees, getting the person to shelter and covering them with a warming blanket will help. Doctors may also administer fluids and a breathing tube, or may apply hot saline into the stomach and bladder through tubes from the mouth and the urethra. For lower core body temperatures, a victim may go into cardiac arrest, but the fight isn’t over: “Even if it appears someone has passed away, it is still important to warm them ... because with this degree of hypothermia the heart can slow to a point at which doctors cannot even detect it. Thus, they could make the mistake of presuming someone dead who is actually still alive.” Doctors will try CPR and other lifesaving measures.

One of the reasons many doctors will not give up on a hypothermia patient when they appear dead is because they may show signs of life when warmed up. There have been cases in which frozen people have been declared dead but were still alive, like the woman from Massachusetts who had attempted suicide and overdosed in a tub of water before being falsely pronounced dead. The San Francisco Chronicle says she was later rescued when an undertaker heard breathing coming from her body bag, helping her narrowly avoid being buried alive.

See also:

Why You’re Always Sick in the Winter

Body Parts You Can Live Without