@Mr. Luigi,
The information from FreeMemory may be useful, but keep in mind, the information is freely available in the Activity Monitor included in OS X. If you want to keep your Mac running as efficiently as possible, you might not want Menubar items running full time. Again, fine for doing an analysis, but not the most efficient thing to do full time after you've already done the analysis.
Also, don't "Free Memory" (unless you really know what you're doing*). Free memory is wasted memory. You're potentially slowing down your system when you're freeing memory.
Data goes from being active to inactive. When more memory is needed it's taking from inactive memory dynamically. Otherwise, it stays inactive and available to be called back into active memory instead of being re-loaded from disk (or elsewhere).
So when you you went from 20MB to 1.83GB of free memory, you really went from 1.83GB of available memory to 1.83GB of available memory. And if any of that 1.83GB of memory was memory you were going to re-use, you slowed your Mac down as it had to be re-loaded.
*There are times when freeing memory makes sense, which is why it's available. Often devs will want to do this, or bugs will exist in some apps where freeing memory can resolve the issue (this is rare). For the most part don't free memory unless you really know what you're doing. And remember, inactive memory is a good thing.