Collapsible fields with Views
To merge fields you should override a template in your view. ( Views 3 and HTML5 - how to override output for markup? )

I'm new to theming in drupal and wanted to merge fields myself to make collapsible fields few days ago as well, but with no luck. Then I used a css-only workaround  without merging fields or modifying any markup. I used it recently in a comision work:

http://aelasoca.cat/web/

The frontpage is an unformatted view using fields. Each 'new' has the standard separate fields in separate divs (Title, image, date, intro-text, category). I used relative/absolute css positioning and opacity to show/hide text and put it over the image. Then with :hover behaviors and changing opacities and positions again I can make appear or dissapear fields. I've used this as reference:

http://www.sohtanaka.com/web-design/css-on-hover-image-captions/