Depends on the employer, but at the least you will be entitled to statutory sick pay(SSP). Most employers will cover the first 5 to 10 sick days without any changes to your pay. After a certain time period this may drop to 80% of wages and then after another defined period of time SSP kicks in, which is usually significantly reduced pay but you are paid and your job will remain open for you to return.
And to clarify further for the US audience, this first 5-10 days doesn't come out of holiday (vacation) time/pay, there isn't combined "PTO" in the UK; sick days and vacation time are treated separately.
In fact, you even still accrue vacation time while off sick, I was off sick for a year and when I came back HR came to me with the news that I had extra holiday to use the next year because it been rolled over from when I was off sick.
If you're sick while on holiday you can even try to claim the days back although most people don't as that's seen as taking the piss a bit.
The UK also has welfare, depending on how high flying your finances currently are, you may not even find yourself falling that far down the ladder. Obviously not great, and non-trivial, but it's a much softer rock bottom than it could be.
The welfare system has been deliberately broken though. The bureaucratic hoops erected in thr last 10 years make it harder for regular people who need help to get while doing little to nothing about fraud.
I think in many parts of the world, it's abnormal to stop paying someone just because they're unable to work. Often companies try to take care of their employees, especially during their rough times.
But in general you will be paid full wages for intermittent sickness (ie three days -> couple of weeks)
As you are sectioned you will have a doctor's note by default, so there is no chance of being fired. (employment tribunal will back you up on that. However there is a cost(capped at £750) to that nowadays [thanks david cameron, you utter shitfacewankstain])
There are a number of rights for returning to work as well after a long sickness.
Should that fail, there is still nominally a safteynet of universal credit. However that has become rather inhumane recently (thanks again David you shitbag.) but it is not as inhumane as unemployment insurance in the US.
