Invisible and immortal zombies

So basically , I was mining in a mineshaft when I saw some zombies then one poofed into nothing , or so I thought after dealing with the zombies a invisible thing went up to me and starting holding me then went over to my Minecraft dog and killed him , I wasn't able to hit the zombie nor see it no matter where I hit , so I ran
That's About it , so can you see what you can do