what is that !!??

Something got fucked with your GPU, check it.
oh, and yea you should be worried O,O
Advice, turn off your computer, take your GPU out of the CASE and let it cool down, and clean it from the dust and check the GPU board and look if something happend there.

Holy shit , Yes be wary

Local GPU overheat. You need check video card cooler and clean it from the dust.

GPU is fucked. Had the same thing happen!

"Should i be worried?"
YES!

yeah, having particles on your screen usaly means that your gpu is fried :(

Your graphics card has been interfacing without protection.

It is sick, and there is nothing you can do except dig a nice plot for it in the garden and choose some appropriate slow songs in preparation for its eventual passing.

If you clean it, and verify the fan(s) are working, and this still happens, it's dead. You'll need to replace the video card.

GPU problem. BIG problem.

First check the system temperatures. No need for special apps for this now, you can try it with Speccy.

Turn off the system and let it cool down for about 30 minutes or 1 hour.

Remove the VGA and clean the dust inside it with a compressed air spray. You should remove the case for better results but this works OK too. If you remove the case you should apply some thermal cooling paste. But make sure you remove the old one with isopropyl alcohol or something like that.
A good thermal paste would be ArticCooling MX-4 or MX-3.

Clean the entire case and the case fans and also make sure all the fans work OK.

Assemble the system again making sure the fans are set on max (is the fans have physical switch), boot to BIOS and set every single cooler/fan on max RPM.

Boot up the system and hope it works. If not and the card is not covered by warranty anymore you can try the microwave trick. I heard it works if the VGA is not too damaged. BUT DO THIS ON YOUR OWN RISK.

Same thing happened to me when the memory on my graphic card died... give it a proper burial and pay her respects by buying a new one :3

I don't play Minecraft, but it looks to me like you've been invaded by Creepers.
(but actually, yes, what other people said (which I haven't read) and if they haven't said it yet: re-seat your GPU to make sure it's secure (and all connections related to it like the cable to the monitor), and also check its temps -- if you're lucky, that's all it is, and if you're not, it's time for a new GPU)

Hello I'm your graphic card and I'm overheat. I can also die in 1-2 weeks.
If it's overheat, clean it, apply some new cooling paste and check temperatures. If it will do it again and again buy new cooler.
If it's old graphic card like 8600gt it probably dies. You can fix it using oven, but just for a month max 2.

Looks like your videocard is closing its little eyes forever. It's the circle of life

(maybe a faulty RAM due overheating)

If that happened to me, I would be in a big shock!

That is confetti, your screen is probably having a party with some hotass GPU. :3

vram probably died