It could be that your spending is atypical to your usual "pattern".
I had the same from my credit card company once when i spent a lot suddenly.
Why not just contact them and ask what they need??
Click on the words "Contact" at the bottom of your paypal account summary page and use the phone option (if there is one in the country you are in) > click on the "call us" option on the left (fees "may" apply so check the cost with your phone tariff first, as you sometimes have to wait a while to connect).
When you get through don't select any options just hang on till you get transfered to an agent or say the word "agent".
have you considered contacting Customer Service via Facebook or Twitter?
You can send them a personal message from their facebook or twitter pages.