Vauxhall Astra keeps cutting out when gearing down and rev counter weird

dear jill
a real dilemma you seem to have.i'm not being sexist when i ask if you know anything about cars.if you don't, then try to ask a friend,partner,male neighbour or anyone who has a clue about the technical advice i'm about to help you with ( allbeit minimal, as i'm not a auto electrician )
right here goes
the new breed of cars are very much controlled by engine management systems & usualy require to be connected to a diagnostic computer. however simple checks can be made prior to this ( & may save you money ). make sure all the multi-plug connections around the inlet manifold & air intake area are clean & sound & not hanging off, also do the same around the distributor/coil area. next ensure all ht leads are pushed firmly into distributor cap & coil. then locate fuse/relay board & check all relays are pushed fully down & they are all sitting squarely & no brown traces around them ( which indicates they are getting hot ). finally if you are locating the relays for substitution,then look for headings around info area such as idle relay, warm up relay,cold start relay, rev counter relay & so on,in fact anything relating to your problem. i sincerely hope my advice helps sort your problem as garages can be a rip off nowadays. if all that fails to help, then try to seek out a bona fide private reliable auto electrician, because they will want to do a good job in order to maintain a good reputation. best of luck love, let's know how you get on, regards dj dave.

does any lights on the dash come on? I've had a similar problem & sticking valve has been diagnosed. been remedied by popping a fuel cleaner into petrol tank & a blast on the motorway in 3 rd gear
hth