That's exactly it - I only do a two or three day tour once a month, so I go from having no sex at all, to suddenly having loads. The first day is always fine, it's always the second one that catches up with me.
The ibuprofen was great, it really made a difference. It's not a matter of being too busy all the time and needing to give my body a rest, it's more a case of going from extreme to another.