I've often been weak while cleansing and now I just let it happen & use the time for restful things. (hee hee, sometimes I even have energy but allot the time to goof off!)
I used to allow myself more "suffering", and I use that word lightly because many truly suffer....But now, if I'm thirsty I'll drink something (but I don't recommend it if you think drinking something could create more suffering/nausea, etc.) and in general I try to make myself as comfortable as possible. For some, that means keeping some soothing pads nearby if their bottom starts to hurt, etc. I rehydrate with Watermelon usually after the cleanse.
This is time for you & your body. Congrats on a great start and good luck with your cleanse!