Aerials in the loft are certainly not ideal, BUT, since the analogue signal was switched off the digital signal was boosted about 1000 times more than it was running at beforehand.
I've always recognised this as a massive con, because for 4 years everyone was told they might need a new digital aerial, which a lot of people went out and bought 'cos that's what they were advised to do, when in fact it just needed to be pointed in exactly the right direction with no obstructions, otherwise the picture would break up or you would lose groups of channels.
The fact is, when digital was switched to full power you should basically pick up a signal with a coat hanger, or your old aerial, because the signal was boosted so much.
I have an indoor aerial in my bedroom that has always worked perfectly, but it has the advantage of being pointed out of a window in the correct direction.
Having aerials in a loft will drag a signal down quite a bit, but if you say it happens every night then maybe you can ask a neighbour if they get any interference, or is it just you?
Do a rescan on your channels too, now there is no excuse for you not to get a 100% strong signal on every channel, unless you have an obstruction, or a loose connection.
Don't rule out animals either, i was helping my neighbour with his recently new tv, as he couldn't get the HD channels to work, and i eventually pinpointed the issue to be between the house and the outside aerial, and found that either a rat or squirrel had eaten into his brand new aerial cable, the bastard.
Here's a helpful guide of things to try.
http://www.radioandtelly.co.uk/freeviewhelp/interference.html