You can't actually bid against yourself. You can increase you former bid, but unless someone bids against you (or you reach the reserve, if there is one) your bid as shown on the listing page will not increase.
Your bids will be visible on the full bidding history, if you view it.
It's not uncommon for bidders to increase their maximum bid, even if no other buyer has placed a bid yet. Some buyers do this deliberately to intimidate other buyers into thinking that the bidder has placed so many bids that there's no point in bidding against them!
