Yay! Paypal finally answered me. This is what they said:
"Thanks for contacting PayPal's Customer Support. I realize that this situation can be frustrating, and appreciate the opportunity to help you resolve this issue.
"I understand that you are having difficulty paying for eBay items. We are aware of the intermittent error 3005 in the eBay checkout flow. We are currently working to get this resolved. Please send the payment using the PayPal checkout flow. "
Then they list a FOURTEEN STEP instruction guide for doing their "flow", whatever that is. I'm probably too stupid or adhd or something to follow fourteen steps! Probably will just contact sellers and see if I can mail a check. I'm so glad it wasn't hijackers in my account though! Phew!
Thanks so much for the help. I was getting really nervous about it...