This thread puts me in a terrible These Kids Today mood, and gives me the urge to answer theinev's question by saying, in some sort of stodgy advice-columnist voice, that if you aren't mature enough to be comfortable asking for a time out to remove your contacts, you aren't mature enough to be having sex.
But really, this has never seemed like a conundrum. If the following activity is likely to be sleeping, I take the contacts out. If it is likely to be awakeness, I leave them in. It doesn't really seem to be all that hard to predict. I think you can feel confident that it is safe to decide between glasses and contacts on some other basis.
Easy on the little guy! It all comes down to this: if your contacts are in and your at her place, and didn't expect to be there, and you do the thing, just sleep in them or if it's appropriate, head on home. If this is a regular thing, carry your case with you, do the thing, get up to use the bathroom, and take them out.
At your place? Take them out. Do the thing. Sleep soundly.
My biggest what the hell do I do with my contacts have happened when I'm called to the hospital for a friend or family emergency and it stretches on to an allnighter. If the hospital pharmacy is open, I could buy some stuff. If not, I've been known to take them out in separate paper cups, soaking in water from the water cooler.
Also, if those are held on with magnets, I would think you would have constant problems with them getting brushed off or falling off. Unless the magnets are really, really strong in which case pain at the piercing point every time they get brushed or struck. Narcoleptics maybe shouldn't wear these.