Sticky Mess

If you're on a mount when you get hit by the Parasitic Attachment, then you are in for a surprise.

You're mounted so you cannot use 1 to "Pull It Off". You're also disoriented so you can't dismount or do anything.

Logging out or Exiting is not possible (you get the "You can't Logout/Exit right now" message). You can do a hard crash but when you re-start WOW you'll be back in the same position - on your mount and disoriented.

It took me a long time (15+ minutes) to figure out that the only solution is to click on the "Mount" symbol in the upper right hand corner of the screen. Then you'll be dismounted and can beat the parasite.

Sticky Mess located at the Deadwash flight point sounds like it's straightforward:
Remove 12 parasites
Seal 4 crates

Some [npc=141332]s are killed or removed from animals and people by a mouseover, others require "pulling the leg" of the parasite (pull by moving away from it).
Then there are the [npc=141332]s that will jump on you, rendering you "Disoriented". You walk around in circles with a parasite on your head and can't control your character.

The cure

• When you are disoriented you're in the parasite vehicle. You have one ability: a flex icon. It's called Get it off.
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• Clicking once, twice does nothing.
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• Click “1" the number of times shown on the parasite icon (stack size). Look near the quest description.
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• You're free.

...You can be re-infected.

Or, your bar may have just changed to have a single button on it. Spam [1] multiple times to get it off your head!