Rough order of events..
• Suddenly felt deep equanimity in my life "nothing matters, but im fine with it" sort of thing. I guess I gave up and was done with everything. Who knows why this happened to me. I wasn't meditating at the time.
• Rather than feeling more depressed I felt a great relief.
• A few days later I experienced 'headlessness' ala D. Harding (had read about it in waking up by sam harris). I was swimming laps in a pool. I was able to investigate it deeply and found (emptiness) the most interesting... and of course clamoured to keep this going..
• A few months later, did a 10 day vipassana day retreat where I better got a grip of physical sensation and again could rest my attention in the present / in my body for long stretches
• Now I suppose I am awakened/enlightneed? I forget it constantly and also need to remind myself not to cling onto it too much.
• Any tips for making it easier to remember or to calmy center myself if I get overly emotional?

People throw around the terms awakened and enlightened pretty much interchangably online it seems, but to me awakening (in line with your experience) indicates an initial degree of attainment on the path, whereas enlightenment is The Grandmaster of attainments and only occurs at the end of a long and comprehesive process of meditative insight. 

As far as your experience - sounds interesting!  Do you have an ongoing practice?  Consistently applying meditation / mindfullness techniques is one of the best ways to deepen and refine initial experiences on the path. 

That experience of being headless sound really pleasant.

"• Any tips for making it easier to remember or to calmy center myself if I get overly emotional? "

It's a pleasant experience to remember it, right? And if it is pleasant, it becomes natural and effortless to remember it more and more.
You could even think that distraction is not a problem, as it allows you to practice repetition on returning to that pleasant state.
A cue I like to deepen EQ is: Can you allow EQ to investigate for you? Or: Allow awareness to investigate everywhere, on it's own.

yes, it is pleasant to remember. That's a nice way to frame it - rather than forgetting or getting distracted, you get to experience it over and over again.
I think i understand your cue. I read something recently where someone said he was washing the dishes and was very distracted and rememberd that the dishes are always meditating.

Hahaha, those are some cool dishes!

The idea of distractions being natural and conducive to better practice is stolen from transcendental meditation by the way. I never got direct instruction from them, but it's a nice attitude I collected from them.

It's funny how repetition can be more fruitful than duration sometimes.
In strength training, the most powerful, effective, easy and simple method I have ever found to build strength is called "grease-the-groove" (GtG) or consolidation training.
You can do 5 good pushups? Do 2 or 3, as often as you can every day of the week, as intensely and precisely as you can, while staying as fresh as you can. If you ache from acid or fatigue, skip a day.
That literally works 10x faster than conventional struggle-till-you-fatigue workouts.

"By letting it go, it all gets done; the world is won by those who let it go, but if you try and try, the world is beyond winning." - Lao Tzu