Okay, thanks. I'll let you know how it goes. I suppose that could cause an intermittent problem because the pool switches cryptocurrencies regularly, if so then that would explain why it's fine sometimes and not others. I'll also have a look next time to see if the pool has switched to mining FTC when this happens.
Anyway, I really need to go out and hunt down some food before I fade away!! Going for a walk instead of endlessly sitting in this chair sounds like a healthy idea too. Thanks everyone.
Another thing to consider is that maybe some other device on your home network is choking out your internet connection. Run "ping -t pool1.us.multipool.us" and see what kind of ping times you are getting. If they are more than 100-200 ms, it may be a network issue on your end.
One-by-one, go around the house and either disconnect, disable wi-fi, or power off anything that is using the connection. Computers, cell phones, DVRs, TVs, gaming consoles, etc. If the ping rate drops significantly when you turn one of them off, it might be causing you problems.