The feeling you get right after being separated from the person you love, such as through saying goodbye after spending the day or night together, especially when it was particularly romantic throughout, or at the end before leaving. You start to miss them horribly even though you were just together, and you can't think of anything but them, or focus on anything else but the time you spent together. Zoning out, feeling like there's a knot in your chest, being anxious, and generally being really happy and/or sad about both the time spent together and your not being with eachother like you were earlier are common symptoms.
To compare, it's like literal drinking. After sixteen beers (or kissing, snuggling, sex, or otherwise romance in general) you can't simply stop drinking and decide you're no longer drunk, you will still feel the affects of said drinking (or again, in this case, kissing, snuggling, etc.) and must slowly wind down from the earlier events.
"God I miss you so much right now, I wish you could be back here with me.."
"I know, I want you back so badly.. I'm completely lovedrunk right now.."