A snapshot of the system is taken about four times per day and it may be that you can recover most of your changes by clicking on the latest of the versions available. Right click on H: drive and select 'restore previous versions'. This should be used with caution as new files may be overwritten with older versions. More information may be found here.
If you have been working on a document which is an email attachment, any changes you made will not save and there is no way to recover the changes. You need to re-open the document, save it to your H: drive and then work on it.