Hey Fraddy!
Congratz on taking the leap into Ketosis! I cover a lot of the expectations going into Ketosis and the science behind it on my facebook page (www.facebook.com/KetoLiving); that said, here is the most relevant excerpt for what you're looking for in your situation:
3) Hydrate! Especially when you withdraw from carbs, you will expel a LARGE amount of water weight initially (your body is expelling the excess glucose in your system in the absence of insulin). This is the reason why you lose so much weight initially. YOU WILL GAIN THIS WEIGHT BACK!!! People think that this lifestyle doesn't work because they regain the water weight under ketogenic conditions, and they completely plateau for a week, maybe 2. This is completely normal.
4) Supplementation. This is a bit of a gray area, but a lot of evidence shows that people benefit on a muscular level (especially through the transition phase within the first month of cutting carbs) to supplement with extra sodium, potassium, and magnesium. Failure to do so WILL very likely result in lethargy, brain-fog, and mood disorders. You need these electrolytes in your system to keep your muscles and brain functioning normally (especially potassium).
Hope this helps. If you have any further questions, the website that I'm making is to consolidate a lot of the scientific studies I've come across (most of which are posted across my facebook page) with commentary as well. If you have questions not answered, feel free to reach out to me on facebook and I'll answer them directly!