Another exciting weekend of Premier League action is behind us and the season only gets more and more dramatic.

The weekend's football was marred by the injury suffered by Hull City's Ryan Mason against Chelsea - a horrendous head injury that reminded everyone that some things are definitely more important than the game itself and we are heartened to hear that he is now in a stable condition and as of Monday was speaking in hospital.

That aside, there was plenty to enjoy. Big teams fell, relegation-threatened outfits bounced back and two of the top six did battle.

It's tighter than ever at the top and the bottom of the table as a result. We're not even out of the January transfer window and already tension is creeping into every game as teams and supporters anticipate the tail end of the season.

With a massive week of transfer activity expected and the FA Cup this weekend looming, this may be the last round of Premier League fixtures with the squads in their current shape.

Here are FIVE lessons we learned from all the action...

 Costa still vital for Chelsea

Football Soccer Britain - Chelsea v Hull City - Premier League - Stamford Bridge - 22/1/17 Chelsea's Diego Costa celebrates scoring their first goal with team mates Reuters / Eddie Keogh Livepic EDITORIAL USE ONLY. No use with unauthorized audio, video, data, fixture lists, club/league logos or "live" services. Online in-match use limited to 45 images, no video emulation. No use in betting, games or single club/league/player publications.  Please contact your account representative for further d

A lot has been said about Diego Costa's relationship with Chelsea over the last two weeks after it emerged he'd had a bust-up with staff at the Stamford Bridge side.

Antonio Conte dropped him for the trip to Leicester but repaired relations last week, unleashing the striker at home to Hull on Sunday.

He showed again how vital he is to Chelsea's title chances, getting the first goal of the game to send the Blues on their way to another victory, eventually winning 2-0.

Their match against the Tigers was especially important considering some of their rivals dropped points in the games played earlier in the weekend.

Arsenal aren't broken yet

Football Soccer Britain - Arsenal v Burnley - Premier League - Emirates Stadium - 22/1/17 Arsenal's Alexis Sanchez scores their second goal from the penalty spot  Action Images via Reuters / John Sibley Livepic EDITORIAL USE ONLY. No use with unauthorized audio, video, data, fixture lists, club/league logos or "live" services. Online in-match use limited to 45 images, no video emulation. No use in betting, games or single club/league/player publications.  Please contact your account representati

Alexis Sanchez's massive and dramatic stoppage-time penalty meant that Arsenal finished the weekend as the best of the rest behind Chelsea with Liverpool, Spurs, Man City and Man United all dropping points.

It looked like it was going to be 'one of those days' at the Emirates Stadium for the Gunners, but again they prevailed in the closing moments of the game.

It's the third important last minute goal in three weeks for Wenger's side with Olivier Giroud banging in massive efforts against Bournemouth and Preston North End in the FA Cup.

Arsenal's resilience is impressive and that should help them in the closing months of the season.

Everton are ready to launch assault on top six

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Arsenal weren't the only team to find a crucial late winner on the weekend with Everton also doing the same at Selhurst Park against Crystal Palace.

Seamus Coleman was the unlikely hero, scoring his fourth goal of the season to give the Toffees a massive 1-0 win away from home.

It's their second victory in a week and the gap between themselves and Liverpool in fourth is now smaller than the one between Reds' deficit to Chelsea at the top.

If they can turn these wins into an extended run of victories they could launch an assault on the top six or even the top four. With four Premier League wins in their last five league fixtures, it's not impossible.

Amazing results against Arsenal and Manchester City have shown they have plenty of quality in their side, too.

Liverpool's exciting nature is their downfall

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Liverpool games are often the most exciting in the Premier League and that was truer than ever on Saturday when a 3-2 defeat to Swansea got the weekend's action off to an amazing start.

It was game that summed up their shortcomings this season, too. Yes they've scored more goals than any other team in the league, but they've also conceded the most of any in the top four.

Their attacking strength is leaving space at the back and, as a result, their defenders are often exposed.

You feel that if the Reds are ever going to be genuine title contenders then Jurgen Klopp really needs to add some defensive steel to his backline. If a team like Swansea, who were bottom of the table before kick-off, can score three against them at Anfield, then better teams will, too.

Bottom six as volatile as top six

Britain Soccer Football - Liverpool v Swansea City - Premier League - Anfield - 21/1/17 Swansea City's Fernando Llorente celebrates scoring their first goal  Action Images via Reuters / Ed Sykes Livepic EDITORIAL USE ONLY. No use with unauthorized audio, video, data, fixture lists, club/league logos or "live" services. Online in-match use limited to 45 images, no video emulation. No use in betting, games or single club/league/player publications.  Please contact your account representative for f

There is of course a lot of chatter about the transient nature of the top six this season, and rightly so. It's been incredibly exciting as Spurs, Man City, Arsenal and Liverpool swap places on a weekly basis.

At the bottom though it's just as, if not even more, exciting. Swansea started the weekend rooted to the bottom of the table and finished it outside of the relegation zone.

They were arguably the biggest winners of the weekend with Leicester, Middlesbrough, Hull, Sunderland and Crystal Palace all losing. The Swans now have a great chance of staying up with Paul Clement in charge.

It'll be tough though and we expect the bottom six is going to be as fluid as ever over the next few months.