Shivering after a C-section or childbirth is very common and usually harmless. Research reviews report that up to 85% of people shiver after spinal anesthesia for a cesarean, and many shake after a vaginal birth too. It usually settles within an hour or two with blankets and warming. Shaking with a fever of 100.4 °F (38 °C) or heavy bleeding needs prompt attention.

Feeling cold during a blood transfusion can come from the blood itself, since red cells are refrigerated at about 43 °F (6 °C), or from a reaction. Chills with a fever are one of the most common reactions, occurring in about 1% of transfusions. Because chills can also signal a rarer, serious reaction, tell your nurse the moment you feel chilled or shaky.

Hospitals feel cold mostly because of the person, not the thermostat. CDC infection-control guidance lists a design range of 70 to 75 °F (21 to 24 °C) for patient rooms, an ordinary indoor range. Patients feel colder because they lie still in a thin gown, may be ill or fasting, and may receive room-temperature IV fluids. Imaging and equipment rooms can run cooler.

Feeling cold for weeks after surgery is common and usually reflects recovery itself: blood loss and anemia, eating less, moving less, poor sleep and some medicines all reduce the heat your body makes. In an Australian and New Zealand study of major abdominal surgery, 59% of patients checked before discharge were anemic. Cold with fever, wound changes or breathlessness needs a clinician.

To stay warm in the hospital, pack layers you control: a robe, a front-opening sweater or zip top that clears IV lines and monitors, warm socks, slippers with non-slip soles and a firm fit, and a soft hat. Leave heating pads and electric blankets at home; many hospitals do not allow them, and nurses can bring warmed blankets instead.

Chills after surgery without a fever are common, especially in the first day or two, when anesthesia, inflammation, pain, a cool room and blood loss can all make you shiver. Chills can also come just before a fever rises, so recheck your temperature. Call your surgeon for a reading above 100.4 °F (38 °C), shaking chills, or chills that start several days after surgery.

IV fluids make you feel cold because they are usually given at room temperature, well below your body's average of 98.6 °F (37 °C), so your body has to warm every milliliter. Anesthesia teaching material estimates that each liter of room-temperature fluid lowers average body temperature by about 0.45 °F (0.25 °C). The arm with the IV usually feels coldest first.