Well pump pressure loss
The Pressure gauge reading cycles between the pump cut-in and cut-out pressures. Sounds like the gauge is dead and permanently stuck at 24psi.

Often, the cut-in and cut-out pressures will be listed on the pressure switch and commonly are 20psi cut-in and 40psi cut-out. So your water pressure on the gauge will cycle between 20 and 40psi during water usage.

The tank has a built-in bladder that is pre-charged to 30psi when your gauge reading is 0psi (pump breaker turned off, water tank drained). There should be a faucet somewhere on the pump manifold system that allows you to drain the pressure tank of water so you can check the bladder air pressure.

To repair the gauge, I would switch the power to the pump off, drain the tank and simultaneously, replace the gauge and check the bladder pressure and top it off if needed. Then power the pump back up. 

If there is a lever on the side of the pressure switch (image below), it is a low pressure cutout to prevent the pump from operating if the well runs dry. Pull it up till the pump turns on and hold till the pump stays on (about 10-15psi). With no low pressure cutout, just power the pump on and it will automatically do the rest.

Once you have a working gauge, you can start to determine whether it is a pump pressure supply issue, or if you have something more serious like a restriction in the house supply line or a leak.

Do you have any sort of sedimentation filter in your water system? Sounds like it may have clogged and if a screen, needs flushed or replaced if it's one of those string filters.