Well, for me it's a past memory -- thank goodness!
But ... what they WERE like was a headache from Hell, frequently accompanied by nausea and not being 100% aware of what was going on around me. My energy during a hangover was for **** and it's only been recently that I've begin to regain some of my former stamina. Even while recovering, my energy would usually collapse after 2/3s of the day was through and I'd have to push myself the rest of the way. I guess I really screwed myself good with drinking.
After a few years of serious heavy drinking I had to limit myself to just a few well-chosen alcoholic beverages because others would give me hangovers that were even MORE unbearable than the above. Tequila, for example, made me wish I could just shoot myself in the head. The pain was mindblowing.