What if my birth control patch fell off?

By 'no protection' I assume you mean no condom.  If the patch falls off the protection it gives isn't going to stop immediately.  It's like missing a pill.  It's not ideal but for one day there is a good chance of getting away with it and as time goes on the risk grows.  Nothing is absolutely safe.  If you use the patch or take the pill or a similar method of contraception you have a less than 1% chance of getting pregnant per year without pulling out or other protection.  The link below is information from the UK health service.  Information on obtaining contraception is specific to the UK.

Please note that a birth control patch IS protection.

People seem very confused about this. All forms of birth control, from condoms to IUDs to hormone-based varieties, are "protection". They are also called "contraception". In other words, in the context of preventing pregnancy, "protection," "birth control," and "contraception" all mean the same thing, no matter what method you are using.

If you are on a reliable form of birth control, you don't need condoms as additional "protection," unless you are concerned about STDs.

As for your patch -- unless it fell off a few days ago, you are probably OK, but since you can't remember when you last saw it, you might want to consider Plan B.

This is not supposed to happen, so you might also want to consider another form of protection.

Since you don't know when your patch fell off this would seem to be a good moment for the morning after pill.

It depends how long it was off your body for. Unless it was several days, it’s very unlikely you’re pregnant. I use the ring, which works basically the same way as the patch (time release hormones), and I’ve forgotten to put it back in after sex many times. I usually remember it later or the next day, and it’s fine.