ultra care flea and tick spray

Question
thank you for responding so quickly. unfortunately today i came home from work and i found him laying in the middle of the cage. he is gone now. i took him to the vet and he claims he could have had a heart attack due to additive stress starting with being taken away from his mother so soon. i still feel as though i'm partly at fault because he looked for me all the time to make him feel safe. and this was the first day i didn't come home on my lunch break and instead was gone for 8 hours straight. i can only imagine what went through his head wondering where i was and if i've abandoned him. he was probably so scared and any little thing could have lead to a heart attack. at least this is what i'm thinking because the vet really thinks it's from being frightened by something. i did the best i could to be his mom. i just feel like i failed. i know people keep telling me not to blame myself but i  can't stop thinking about how i let him down. he looked for me and i wasn't there. for the past 8 days i've had him he was my everything. and i couldn't protect him. i just hope he knows i was coming home for him. and i really did love him with all my heart.
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The text above is a follow-up to ...

-----Question-----
Hello, I just rescued a baby dwarf bunny from downtown la that a dirty person was selling on a cart. he is no more than 3 weeks old. i already took him to the vet and he's doing so much better now.... except for the FLEAS. of course i was suggested advantage or revolution but to wait a few more weeks or so. well i just feel horrible for the little guy living with fleas for much longer (he's quite miserable itching all the time) and i purchased ultra care 8in1 flea and tick spray. i haven't used it yet because i want to make sure it will be ok. i'm so paranoid about harming him. i mean it's for small animals and people even use it for dwarf hamsters. can't get much smaller than that! but still... are there any precautions i should take? there are no age or weight recommendations on the bottle or the website. please please pleeeeease let me know asap. thank you so much for your time!
-----Answer-----
I have never had an issure with fleas on a rabbit. I hate that he is so young and already been exposed to the nasty side of humans. This little feller will have a hard time making it if something is not done about his flea problem soon. On the flea spray... I think since he is soo young maybe take half a bottle and dilute it with water, storing the other half until he gets older and can handle the stronger stuff. Spray lightly avioiding eyes, ears, nose and mouth. Aviod getting it in his water or on his food. And also preferably not aroudn where he will come in contact with it and possibly ingest it. Hopefully it will kill some of the fleas. Too many fleas can lead to anemia which will cause death.
Samantha

Answer
Sorry to hear of your loss.
I am almost sure it wasn't a heart attack though. I would say that the fleas just took too much away from him. He was also really young, and possibley way to young to be away from mom. I keep my babies with mom until they are atleast 8 weeks old. Please don't blame yourself, he may not have made it even if you were there. Look at it this way, he doesn't have to suffer with those fleas now.
Sam