Anxious for Wake and Funeral

My grandpa passed away this week. He and I weren't super close and it was a long time coming-- he's been fighting illness for a long time-- so I can't say I'm super upset about the death itself, I'm glad he's finally at peace and no longer struggling with life.

But my little sister was very close to grandpa and is very emotional about this, so I promised her I'd make sure to attend the wake and funeral to support her.

I'm very nervous about the wake. I have never been to one and don't really know the protocol, but when my aunt passed away in the hospital we were given an opportunity to view her body and it was one of the worst decisions I've ever made. I ended up puking afterwards and I hate that my last memory of her is all cold and grey and small in a hospital bed.

I know the wake will probably not be like that, but I don't know if emotionally I can stand to view the body. I don't know what to expect, will I have to go up to grandpa's casket? Would it be rude if I declined? I'm anxious about doing the wrong thing or seeming insensitive. Does anyone know what I can expect?