So I was walking through the woods at the base of the mountain by dagons shrine when I got attacked by my first elder dragon this playthrough. Thought to myself that it would be a hard fight since I was wearing light armor instead of my usual heavy stuff. But I knew I could do it. As I'm shooting arrows at the dragon I see over ten extra red dots on my compass. Figured a stray arrow maybe went into the nearby town and hit someone. Found out fast I was gravely mistaken as over a dozen vampire related enemies poored outta the woods. Four thralls, four death hounds, three master vampires, two fledglings, and two ancient vampires. Thought about loading a prior save since I knew I wouldn't survive the fight but decided to stick it out. Both enemy attacks were focused on me, so I spent more time healing then landing blows. After two minutes of constant healing the dragon turned on the vampires drawing all aggro from me and finally allowing me to dish out the pain. It took ten minutes to finish the fight with the dragon killing a little more than half the vamp force. At least they took his health down to below half which allowed me to beat the dragon. Wonder if anyone else has been hit this hard by the vampires? Or dawnguard for that matter?

I have been hit hard they came out of nowhere full force this happen to me while I was heading to Markheart I had to jump into the river just to get away from them.

Yup!
Not recently, now that I've finished the Main Quest of the DLC.

While I was running around in the beginning of the content, however, I exited Dragon Bridge heading toward Solitude. I was going to visit that stormcloak camp for some reason, and decided to take the actual path rather than sliding down the hillside. When I reached the cross roads, a band of 6 dawnguard ambushed me as I ran by. Two were shooting their crossbows, two were light melee, two were heavy melee. I think one may have also cast a few spells. They split between me and Serana (I was also a VL at the time), so I started looking for a way I could duck out long enough to change. I ran around a boulder and was attacked by a small pack of wolves.

Only wolves, no big deal, but then a bear came out of no where. For the life of me I don't know why, but I decided to back down the hill toward the town while I tried to work out a strategy and stay alive. They were kicking my ass! When I neared Dragon Bridge, a dragon attack event started. So now I have 6 dawnguard, some wolves, a bear and now a dragon attacking.

Luckily for me, Serana was pulling more than her weight and was downing her second DG, the dragon made fast work of the bear and another DG. In the confusion I wiped out the wolves and began pelting the remaining DG with arrows, then killed the dragon. Thankfully he was frost based.

From that point on I made it a point to sneak around that junction in particular, but also sneak as I left any city. Good thing too since I was always attacked

Since then I've had something similar happen a few more times, but again, since I've finished the DLC its been a little too quiet.

^ Whoa I would had simply reload.

(Censored) got vamp swarmed again! Luckily though I got saved by a random occurence and two guards walking by. This time it was six masters, four fledglings, and three ancient. Went running away and had the random event where two vigilants attack a running vamp. So the one vamp joined forces but I gained two vigilants which took some of the aggro. The best part was I was about to die and a guard came running up and cut down the vamp messing me up. In the end my side won with no casualty's thankfully. I always get attacked when I'm trying to level a skill I don't typically use.

I have had tons of random encounters however not in the numbers you are getting. Mine usually come in groups of three. Ancient or Master vampire and two thralls. I have hit three different groups one after another on the same road in short order but they were each separate attacks. After my encounter last group I found a single ancient vampire fleeing from two vigilants. I thought it was a trap but they turned out to be real vigilants and not thralls.

In your attack with the dragon, I wonder if the dragon attracted different groups at once?

If so they all conveniently spawned in the same exact spot and the forest was pretty think, the dragon barelt had enough room to land.

Barely, sorry one my phone at work.

I am 81 I had two death hounds three thralls, Mast Volkihar Vampire, and a Volkihar vampire.

I honestly can't WAIT for these Vampire Attacks everyone goes on about. It will be soooo much fun to use my holy powers in public!

They can be pretty fun as long as you know what your doing. If a npc dies it can svck but ias long as you can handle the situation.