Good news, Bekki. The reassurance you have had here about weight gain is valid, but I can't stress enough that babies who do not wake for feeds and who would sleep for hours and hours if 'allowed' to should be making alarm bells ring - it was the fact your baby was sleeping and not feeding very much at all on day 4-5 that made me respond, not the weight loss which was within normal. However, if you had continued being 'relaxed' about him not feeding, you might have got into difficulties.
Babies who sleep for hours in the early days are not good news.
New babies belong beside their mothers, able signal when they are thinking of having a feed, and close enough for the mother to respond gently and quickly before the baby has dropped off to sleep again. The very fact of being close means the baby's instincts to feed are stimulated. Getting the baby attached so he can feed effectively is easier, too.
Some babies - whether from temperament, jaundice, recovering after the birth, side effects of drugs - are content to sleep away the time, and this can lead to a milk supply that spirals downwards, and poor weight gain.
Intervening, as you did, well before this stage is really helpful.
Hope things continue to be fine