Is this normal?

Just a quick question. I started the PB shakes and I'm into the 2nd week, very excited. But, I've been really tired and sleepy lately and I'm just wondering if maybe it's the cleansing? Mmm I'm constantly thinking of my yummy bed and how nice it'd be to snuggle in it and sleep for a few days. I'm finding it extra hard to get out of bed in the morning and when I get home from work all I want to do is nap. Is this detox? I started on 2 shakes today for the first time. Is this detox going to get worse? It's really not bad, I feel pretty good all in all, just curious about the sleepiness. Oh and I've been doing everything else the same as far as sleep is concerned. Thanks!