The sidebar and all the widgets have disappeared from my home page but are visible on other pages (about me/contact me etc)
Would very much appreciate advice as to how I get it back (asap)
blog is http://helloitsgemma.wordpress.com
They haven’t disappeared. They are all down at the very bottom of your main page.
This is most often caused by an open HTML tag in one of your posts.
Go to settings > writing and select “WordPress should correct invalidly nested XHTML automatically” and then click “save changes.”
Now, starting with your latest post, open it in the editor, make one minor change such as adding and then deleting a space, and then click “update post.” Check your blog and if it is back to normal, you are golden. If not, open the next post and do the same thing till it goes back to normal.