I could have written this post...in fact I did, back when my 5 month old was that age...and a similar post just recently. Same - sleeps a lot but is totally alert when awake and happy and talks etc. Accept that you are lucky and nothing is wrong! (I should take my own advice!) My DS still sleeps a lot! and I still worry about it - but other bellybellers and the MCHN have assured me that what I describe (which is similar to your baby) is normal.