If the arrow is pointing up, then you do have a bit of a problem on your hands. Your navigation menu is stuck. This is what is causing your menus to drop open and your wysiwyg toolbar to disappear.
Click on reply which will load the wysiwyg post editor without the toolbar.
Now press Ctrl + F5 at the same time. This will do a hard refresh of your page. You should now see the toolbar in the post editor.

I can't promise you that this will fix your problem forever. To some people it only takes a single hard refresh to get the navigation unstuck but to others it takes many tries. It is not real clear what is causing this issue.

Can you tell me what browser you are using?

Please let me know how the hard refresh works out for you.