Slimfast & Body Reaction

Hi All. First time visitor, first time poster. I've been on Slimfast
5 and a half days and have lost 4-5 pounds already. Woo-hoo!
I'm pretty excited about it. One thing concerns me though. I started
Sunday afternoon. On about day 3 I started to feel very weak.
Tuesday I had a very mild fever (99.1), a splitting headache and I
stayed home from work Wednesday because I was so tired. I slept from
Tuesday night straight through to Thursday morning! I woke up around
12:30 for a slimfast bar and an apple, and again around 6 for a
sensible for a very light dinner that I didn't really have an appetite
for. I probably could've used the extra sleep even before Slimfast
but I never felt so tired in my entire life. I was worrying I was
catching mono or something. I'm wondering if Slimfast is contributing
to this extreme fatigue. I'm better now. By Thursday morning I was
feeling better. Somebody said I wasn't drinking enough water. As
part of this diet I've also cold turkey quit my 4-6 cans of Pepsi a
day and someone else suggested that what I could be experiencing is
caffeine withdrawal. Any help from anyone that's experienced similar
symptoms from either Slimfast or c.w.?

Thanks,
Seth