Yesterday I was on the 1W26 up from Southampton after the SWML disruption with the freight trains and between Micheldever and Hook there was an astonishingly violent movement of the train, everyone flew around (not helped by it being full and standing) and my partner nearly went straight into one of the doors. I'm used to the usual amount of bumps and wiggling going to London but that was really quite bad to clomp at full speed.
Do you think it was Worting Junction, around 3 miles before Basinstoke? It's always a bit rough going over those points from the Up Southampton to Up Fast. I've been on trains where the guard has done a PA annoucement to advise people standing to hold on.
The line speed is 90 and the points are also rated for 90mph.
My initial thought was Worting Junction, those points on the Up Winchester, leading to the Up Slow and Up Fast. 90 mph as Vexed says, and although not too obvious on Google, they are (or were in my experience) a very long 'Y' turnout , and so which ever route is being taken, a train will (probably) suffer similar ride qualities.
How bad is bad?
Having ridden (last century) through there on loco's, the ride through those points on class 47s was nothing to worry about, possibly due to 47's having 6 wheel bogies? But on class 33's when going through those points one could almost be bounced out of the seat. This may have been partly due to 33's having only 4 wheel bogies (as per 444/450) and being lighter in weight than a 47?
For drivers (in particular) there is a chance of complacency perhaps, knowing that historically location X is usually a bit rough, but that said any driver who suddenly feels a certain location is noticeably rougher than it was 'yesterday' (so to speak), will most likely report same to signallers, who can then put a temporary line block in place for said location to be examined, or deal with as seen fit.
As far as the OPs journey (ie on SWR) is concerned, ie: where Guards are still employed, if concerned about any such matter, first port of call is the guard,
at the time concerned, don't wait until the end of the journey, and don't be embarrassed about raising any such matter either.
A further memory from many years ago: On the Down Fast between Byfleet and NH and West Byfleet there was, for some months, a section of track that caused 158/159 units to experience quite bad 'hunting' (ie; side to side knocking , in the passenger saloons), which I myself reported to Control when I first experienced it, but strangely, as far as I recall, 444/450's were not subject to the same.
Update - my BOLD: reporting at the time concerned should allow the guard to identify the approximate location by looking out the window, something that few passengers can do without the aid of station name boards, which may not be readable at speed etc.