Only had the flu twice, once when I was 14 and then this last time. Although It seems that January/February is my 'sick months' for the year. I tend to get hit by something hard almost every time.
Night sweats were cause by both, the fever from the flu caused bad sweating. Trest also caused it, but not until the 75-100mg/day range. It wasn't bad, but I hate night sweats so I make it out to be worse than it is. I checked my body temp twice a day while sick, just to make sure I was getting better because you feel like shit all the time with the flu. Once my fever went away and my body temp was normal, night sweats stopped. After I felt like I really kicked the flu, I started the trest back up and the night sweats came back on.
I have to say though, that night sweats is NOT a common side effect of trest. It may just be how my body reacted to it, so keep that in mind.