Professor Keith Willett, NHS England's national clinical director for acute care, has highlighted the dangers of storing up health problems over the festive period.
He warned of "an outbreak of misguided stoicism" during Christmas and New Year.
Prof Willett said every Christmas, thousands of people delay seeking help until after the holidays, ending up more unwell than they might have been. These delays often result in people being admitted to hospital as an emergency, he said.
"Many of us enjoy celebrating the traditions of Christmas each winter but, as a doctor, I know the equally predictable increase in illness at this time of the year can be a danger, particularly for our older and frail citizens," he said.
"We should be doing all we can to stop illnesses starting by keeping well and through vaccinations but also by responding promptly when illness starts, particularly in those that are vulnerable.
"There is often a desire to soldier on to the New Year, to avoid the holiday being interrupted, not to 'make a fuss', 'bother the Dr' or ask a favour of friends and family. My message is simple - if you feel unwell, do seek help or advice early, nip it in the bud and prevent it becoming more serious."
He added: "My message is simple - look after yourself and others this Christmas. If you, a friend or relative does feel unwell over the holiday, do not soldier on to the New Year but seek early advice.
"The NHS is available 24 hours a day, every day of the year - you can go to NHS Choices website for advice, or use your local pharmacy or call NHS 111.
"If your symptoms don't get better make an appointment to see your GP - remember there is always a GP on call out of hours covering your area and if necessary they can arrange for a hospital assessment."