"Why does it seem familiar? Is it because of past lives?" could be, who knows...
Perhaps a more important question is "what are the causes for these meditative experiences to occur?"
Also, "are these experiences useful in any way?"
These two questions should help you to identify useful phenomena and to be able to set up the conditions which lead to the arising of such phenomena. Certain mental states such as joy, tranquility, clarity are all useful and you should learn what leads to the arising of these states so that you can re-create them. Various perceptions you may experience (such as the body ballooning out, floating, feeling like stone, etc) are not necessarily useful in themselves, but they may be a sign that your meditation practice is deepening and you are letting go of your body. Don't worry so much what occurs in each particular meditation session, instead focus on the attitude you bring to meditation (is it an attitude of craving or an attitude of letting go?)
I hope this info is useful to you.
Four types of letting go:
1) Giving; expecting nothing back in return
2) Throwing things away
3) Contentment; wanting to be here, not wanting to be anywhere else
4) "Teflon Mind"; having a mind which doesn't accumulate things
- Ajahn Brahm