If you've been trying to keep up with the Brexit developments and are starting to feel dizzy, don't worry. It's all very confusing and moving faster than is really good for you. However, here are the answers to some key questions, which might help you back to your feet.

What's just happened with Brexit?

In short, Boris Johnson has pulled off a massive coup. After being told repeatedly that he would be unable to renegotiate the Brexit deal that his predecessor Theresa May struck last year, the Prime Minister has done exactly that.

It seemed unthinkable just weeks ago, but Johnson has convinced the EU negotiators that the only way he could sell a revised deal back home was if they removed something called the Irish border backstop, a mechanism that seeks to keep an open border on the island of Ireland.

What's in the deal?

It's basically the same deal as May's, but with some tweaks to the goals for the future UK-EU relationship and, of course, the replacement for the backstop. The new Northern Ireland protocol is extremely complicated but, in short: Northern Ireland will be given special status, recognizing the unique history of the island of Ireland.

Under the new plans, Northern Ireland stays aligned to EU rules in certain areas, while remaining fully part of the UK's customs territory. How it actually works will be highly controversial. But, it's not the backstop, which should help Johnson succeed where May failed.

Is that it? Is Brexit done now?

If only. As stated above, it should help Johnson succeed, but it probably won't. The main reason that May struggled to get her deal through Parliament was that it wasn't supported by her Northern Irish allies, the Democratic Unionist Party (DUP).

The DUP believed that the backstop paved the way to Northern Ireland uniting with the Republic of Ireland and leaving the UK. For unionists, this is a non-starter. The problem is, Johnson's backstop replacement arguably makes this a more likely outcome. And that's why the DUP has said it would be unable to support Johnson's deal in Parliament.

What is the DUP and why doesn't it agree with the deal?

The DUP is a Northern Irish party which is very conservative and very pro being part of the UK. Their members, for example, oppose abortion and gay marriage, in contrast to their Conservative allies in London. The DUP's priority throughout the whole Brexit process has been to ensure that Northern Ireland remains fully a part of the UK. It doesn't matter if that happened through no deal or a very soft deal.

The problem for Johnson is that his deal puts a border in the sea between the UK and Northern Ireland. But it also contains something called the consent mechanism, which would give all Northern Irish political tribes the opportunity to consider its position at regular intervals. The DUP fear is that a republican majority could take control in years to come and force Northern Ireland out of its beloved Union.

Has Boris Johnson just done what Theresa May couldn't?

No. He's done exactly what she did, so far. Moving on from the DUP, Johnson also faces opposition from hardline Conservatives in his own party. They previously used the cover of the DUP to vote against May's deal which they thought tied the whole of the UK to Europe and betrayed the Brexit vote. It seems unlikely that Johnson will be able to square his hardliners off, especially when you consider that his deal still commits London to pay Brussels £39 billion in its divorce bill.

And it's extremely unlikely that any opposition parties will try to help dig Johnson out of his hole in Parliament. Which is a massive problem, when you have a working majority of minus 40.

None of this, of course, will be missed by those watching in Brussels. The deal, it should be remembered, has been agreed by EU negotiators. On Thursday evening, the actual leaders of the member states will get together and discuss whether they want to agree to this deal.

And as one EU diplomat told CNN on Thursday morning, “our main concern is that Boris Johnson turns out to be Theresa May 2.0.”

Johnson has a long way to go before he can pop open the champagne. He's got to get through his first EU summit, a famously brutal arena. He's got to face his own party members and his DUP allies, who might well accuse him of being a sell-out. And he's got to sit in Parliament and with a straight face tell lawmakers they should vote for a deal which looks a hell of a lot like the one Johnson himself voted against twice.

Johnson's optimism has taken him further than anyone expected. But, as ever with Brexit, at some point gravity will bring you crashing back down to Earth.