Motor stopped while vacuuming (Electrolux Z1373)?

I've had my Electrolux Z1373 for more than 13 years. For the last few days I've been doing a lot of heavy vacuuming in the loft prior to laying insulation. Over the last 24 hours I noticed a different sound from the motor - seemed to be a bit more of a higher pitch - but it was still sucking alright.

I don't know if this is relevant but I was standing on a pair of steps, with the upright balanced on the top step support (the top step is missing) when the motor just cut out. I've checked the fuse but it's ok.

I replaced two of the filters yesterday but I didn't have a relacement filter for the one that goes in the back - I think it's called the hepa filter and it's absolutely clogged with dust. Could that be why it's stopped working? If not, does anyone have any other suggestions or ideas as to whether it's fixable and if I can do it myself. Many thanks.