Edward,
Question for you. Is this sluggish behavior recent or long term? If you have a Windows machine you might be able to use one of the earlier restore points that the computer makes to restore the computer back to before it started to do this. It will not destroy your information just roll back to a time before the computer started to act wonky.
You need to see if you have any hard drive space left. Your computer uses your hard drive space as a kind of extra memory and if the hard drive is all full then it has to wait for the normal memory to empty a bit before it can proceed, this can cause your sluggish and freezing behavior.
Another thing to check is to get a program that detects and disinfects your system from programs called malware. Essentially these are unwanted programs that while mostly benign can clog up your computer. You can get a decent but free anti malware program form the link --->
https://www.malwarebytes.org/mwb-download/. Install it or a program like it and run it. It might do the trick for you.
DW