Quite a lot of people report feeling tired after a flush. I'd think the body needs time to recoup.
I am not familiar with the dietary restrictions associated with the flush you are following, but might be possible that you need to provide minerals for your body.
From what I understand, magnesium may be depleted during a flush as may be other minerals, so this would be one thing I would look into.
That "lead" feeling may be just because of the fact that you kept the salt on for longer than indicated, and the body may have released too many toxins into the system. I believe that jumping into a hot shower for some 10-20 seconds then turn it to as cold as you can possible make it will stop the detox process, and give the body time to unload the toxins.
Mineral depletion may also be the cause of the water retention you seem to be experiencing. I believe that you must balance the sodium/potasium/magnesium intake? Maybe you can look into that. Or post a query?
I usually check the Ask Moreless site for some very good guidance, but be ready to get some good lickin's if you don't pay much attention: like good teachers of old, he expects you to figure things out and do your part too.
(I'll post the links for ratios if I get sometime later on.)