Yes! I felt exactly the same. Pretty down because my body was struggling to adjust so was having cramps, back pain etc, but still completely determined to carry on.
I think the secret is to take it one day at a time. Personally I find the thought of going without solid food for the next 12 weeks completely daunting/depressing and I can't imagine I'd achieve it but at the same time I know that I'll stick SS 100% for the next few days, which should turn into the next few weeks and next few months...
Take time to treat yourself - have a facemask/manicure, a trip to the cinema/ whatever makes you happy and just focus on the next few days. You will feel better, I promise. I'm on Day 7 now and feeling alright.
Look after yourself...
x