Games normally come in pairs against the same opponent (Tournament, clan challenge, and clan league games) if you move in both games at once I think it tends to have a stabilizing effect on your rating. The tendency is to put off games that have become difficult, and to play faster in games which are easier. This means that you tend to start accumulating losses. Attempting to keep pairs of games in sync helps to offset this effect. I try to do this and my rating is relatively stable, in that it normally varies by less than 100 points (ie 1775 +/- 50), whereas a lot of players have a far greater variation in their rating.
Although I agree that your form varies of itself as well, this is going to be more relevant to OTB games where you finish the game on the same day. In correspondence games you'd actually expect the game to be spread over that kind of fluctuation anyway so it should average out. I think the antidote is to realise you're in blunder mode and stop moving for the day.