I've had very similar, 4 times over and potentially more blood than you describe. All times it felt like I had literally wet myself big style!!
First time was in the middle of a supermarket on Boxing Day, thought tad embarrassing to loose total bladder control at only 11wks pregnant, until I looked down to see blood streaming down my legs in a scene that looked like a horror film! Another time was in the middle of the night (never thought a new king sized mattress would be on my things to buy list during pregnancy!), third time at the mother in laws (now that was embarrassing...) and fourth time just at home.
Each time (at 11wks, 13wks, 14wks and 17wks) huge amounts of blood that overflowed a sanitary towel and streamed everywhere, but always just bright pink or dark red, with pink/brown spotting that carried on for a week or two afterward.
And yet despite all of that, here I am at 30wks, with two twins currently having a fight amongst themselves in my belly!
I was told in the hospital which might be reassuring for you, dark blood (very deep red/Brown) is old blood, so whatever the insult was it has already passed a few days ago. Pinky blood or bright red blood that is without clots is likely to be your blood, so from cervix, uterus lining etc and you have a lot of blood to loose before it causes you an issue. Only time they really freak out is if the blood clots on toilet paper or pad once out of you, or if it is coming out in clots already or has grey tissue like bits in it, that's then potential baby/placenta blood loss.
So take a bit of heed in the fact it's bright red and not clots, it's likely blood from you not baby, but obviously every time it happens get checked out ASAP just in case. Do expect spotting for at least a week now afterwards, so long as it doesn't fill a sanitary towel within an hour they really aren't bothered about it at all. Apart from me needing Anti D jabs, bleeding just became part and parcel of my pregnancy until 20wks when it all just stopped as suddenly as it started, it was an overnight transformation, really weird. Consultants never did find the cause...