Help Please! I Woke Up With A Quarter-sized Knot On My Forehead. What Could This Be?

I woke up with a big red spot on the top right corner of my forehead. I thought it was from pressure of laying down, because I only saw the redness. One hour later I look in the mirror and the redness is gone, but I can see and feel a huge knot! It looks like I rammed my head into something.

I used a Vitamin C serum recipe on that side of my forehead (1/2 tsp Ascorbic Acid, 3 tsp distilled water) last night for the first time... BUT I have been using another Vitamin C recipe before that for about a week, similar but the only difference is it was included with Glycerin. I had no problems with that, so I have no idea what's going on.

I have no remembrance of hitting my head into the wall or anything, but that's what it looks like. I'm pretty sure I would remember if I hit my head hard to do some damage like this. Doesn't look like a cyst or anything acne-related whatsoever. I've had acne for 8 years so would know the difference...

I'm freaking out because it's badly swollen up and I don't want it to do any permanent scarring or anything. Any ideas? Thank you in advance!
It's definitely not a boil though. It's not painful nor discolored...