The first rule of writing about Bitcoin is: don't write about Bitcoin.

The story of the world's best known cryptocurrency is astonishingly fast-moving and its fans will soon line up to tell you you've got it all wrong.

But write about it we must, because the past 24 hours have been catastrophic for the grande dame of cryptocurrency - even by Bitcoin standards.

I'm going to concentrate on Bitcoin here - but if you're a crypto follower, you'll know the whole market is troubled, to put it mildly.

What's happening?

As I write this, Bitcoin is trading at $21, 974 (£18,000). It's fallen 25% in the past five days alone, to its lowest value in 18 months. Its peak of almost $70,000, in November, feels a lifetime ago.

The charts are all red and they're going in one direction - downwards.

Experts say this is because of the wider global climate. It's not just in the crypto world things are not looking good.

Recession looms, inflation is soaring, interest rates are rising and living costs are biting. Stock markets are wobbling too, with the US S&P 500 now in a bear market (down 20% from its recent high).

As a result, even the big investors are less free with their money. And many ordinary investors - not rich hedge-fund owners or corporations but people like you and me - have less to invest in anything, full stop.

For many, an investment in something as volatile and unpredictable as cryptocurrency feels like a risk too great in these times.

It's unregulated and unprotected by the financial authorities, so if you're using your savings to invest in it and it loses value, or you lose access to your crypto wallet, your money has gone.

Why now?

Last month saw two much lower-profile but nonetheless significant coins collapse - and this knocked a lot of confidence in the market overall.

As a result, people are increasingly deciding to sell up.

The more people sell, the less Bitcoin is worth, because that's how it works - its value is pegged to its desirability. This has a knock-on effect of more people selling because they can see the value going down... and the cycle continues.