Dr Mannix, 64, shared her expertise on death on BBC’s Woman Hour alongside radio host Emma Barnett.
The retired doctor, who released a short animation Dying For Beginners, explained the process involved in an ordinary death.
“The first thing that’s noticeable is just that the body starts to run out of energy,” said Dr Mannix.
The specialist compared the ageing body to a mobile phone battery that “won’t stay charged”.
The charger in this case is sleep, which provides more energy than food or drink.
“In fact, a lot of dying people don’t feel very hungry and that’s fine,” said Dr Mannix.
“They’re not dying because they’re not eating. They’re not eating because their body is dying.”
As time goes by, people gradually require more sleep to have the energy to think and do what they can.
During sleep, people tend to fall into unconsciousness, but they won’t recognise that this is happening.
“It’s not a frightening mental state to be in, it’s a state of not knowing anything,” Dr Mannix assured.
As the body enters its final moments, the person becomes unconscious “all the time”.
Rather peaceful to go through, onlookers may be frightened by what they hear.
Known as the “death rattle”, a person falling completely unconscious may sound as though they are struggling with laboured breathing.
Dr Mannix explained: “The brain runs reflex breathing patterns that move backwards and forwards between quite deep breathing that gradually becomes more shallow.”
It may appear as if the dying person is breathing fast, but shallow, but this is a sign of “deep unconsciousness”.
“This person is quite safe,” said Dr Mannix. “There will be a breath out that just doesn’t have another breath in after it.”
Dr Mannix said she’s on a mission to “take away the fear” of dying.
