"I can't believe the behaviour my BF explained I was doing after midnight on NY. Granted, I had had a fair amount to drink, but not the first time in life I've had a fair bit. The trouble is I have hours missing where I apparently flirted with others in front of my BF (really not like me, I was very happy with my BF), then made out with his work colleague right in front of him and when asked by him to come away with him refused. I have no memory of what this work colleague even looks like."
I used to be a massive binge-drinker used to 'brown outs' (where you miss chunks of an evening but can usually piece together most of what happened, especially when prompted. 'How did we get home?' 'Don't you remember? We got in that taxi and you were singing Adele to the driver?' That kind of thing).
A blackout is different. You can't remember even when prompted. Its a result of the rapidity of the rise of your blood alcohol levels which isn't just dependent on quantity and time but other factors too. Your brain is literally unable to form memories of what you're doing but you continue to 'function' in terms of walking, talking etc so most people would see you as drunk and possibly acting out of character as very drunk people often do, but not incapacitated.
I, and my friends were routinely very pissed on nights out and not unusual for us to forget chunks of an evening but hours-long blackouts (which can occur just with alcohol were rare).
I was well used to drinking a lot, as you, but the first time I had an en bloc blackout I thought i'd been spiked as I 'came to' walking around town after dawn without my handbag and wearing somebody elses coat then tried to get on a bus with a Superdrug receipt as thought it was a return bus ticket. When I got home and called friends (I have a list of numbers written down and an old handset with PAYG for emergencies, plus a front door key hidden in the garden) I couldn't remember at all the last place we'd been drinking in, let alone the next few hours but they said I had seemed drunk but not so much that they'd refuse to leave me and I had refused to go with them when they left. Reported my lost handbag and 'phone to the Police and the pub and concluded i'd been spiked. Though my friend at the time did say 'yeah, you spiked yourself with a bucketful of lager'.
Happened again another time and the 3rd time, I 'came to' at dawn (outside all night drinking place' I couldn't remember entering) and was talking to some guys that seemed aggressive and who I assumed stole my handbag as I no longer had it and then I heard them smash windows going up the road.
I remember calling the Police and I sat on the kerb for 2 hours waiting for them to arrive while periodically calling them back to see how long they'd be and crying to the call handler about my awful night. The Police arrived and I told them I thought i'd been spiked for the purpose of stealing my handbag. As they drove me up the road, I couldn't see any broken windows so thought I must have heard a bottle or two smashed and thought it was windows which confirmed in my mind, I must have been slipped drugs to have such distorted memories. I was taken to hospital and blood tests taken which just showed high levels of alcohol, though they can't test for everything.
Couple of weeks later the Police came to follow up as i'd reported a crime. I'd told them where I remembered being before the last place and CCTV showed me leaving my handbag in one place (which was then swiped by someone lol) and in the place I couldn't remember being in, the barman remembered me ordering a drink then having no money to pay for it and me becoming aggressive claiming i'd already paid (v, v out of character for me to be aggressive) so I was chucked out and hung around outside for ages outside annoying people going in or coming out for a cigarette, asking them to buy me a drink and complaining about the barman (again, out of character and very embarassing).
No recollection whatsoever. Could I have been spiked? Possibly, but it seems far more likely I was just really pissed and despite denying it the first two times I had had an en bloc alcohol induced blackout, I addressed my drinking the third time as it was very unlikely to my mind, that I'd been so unfortunate to be spiked by these mysterious spikers that give drugs away for a laugh on 3 seperate occasions.
You might have been spiked, no-one knows. But that would be rare in comparison to the number of people who just got really pissed and thought (or wanted to think) they had been.