So I tried this about a 18 months ago using unchained to fund a family vacation and personally I didn't like the experience. I was always worried about having to post additional collateral and then at the end of the loan I needed to either pay back the full amount of fiat or roll the loan to avoid selling my bitcoin.
My advice would be to get a loan in the fiat system. I'd recommend that you borrow against your home or your retirement account before you borrow against your bitcoin. Could also borrow from family or friends.
All that said, borrowing against bitcoin in a bull will be much different from a bear.
Just my 2 sats.
Good luck!