Lost all my posts and photogallery installing Next theme

Hello,
I blog on food (in french) since 10 years on cuisinepublique.net. Last time I changed theme was 2 years ago (food press) that is not available anymore. Looking on the net I found NEXT theme that I seemed fit all my needs.
I logged in wp-admin and, thinking to install next-pack-siteorigin-com.zip installed instead site-origin-panels.zip (thétique I don’t remind to have downloaded). And, surprise, all my posts and galleries have disappeared. The only gallery is the one of the NEXT theme. I’m a little in panic, since I would be quite unhappy to have lost hundreds of posts.
Is there a way to go back one step and have my database back?