Some of these functions are not available when other options are set on the camera. HDR and handheld night mode aren't available if you are saving the images with the Quality set to RAW or either RAW + JPEG option. It doesn't work with still pictures when in movie mode. HDR is also not compatible with the Time Lapse Shot or Auto Shoot in Stop-Motion Mode. I'm not sure if there are similar limits with the Panoramic shot mode.
See the advanced manuals available on the Panasonic Lumix DMC-FZ300 product page, http://shop.panasonic.com/cameras-and-camcorders/cameras/lumix-point-and-shoot-cameras/DMC-FZ300K.html
, for these restrictions. The direct link to the manual is currently ftp://ftp.panasonic.com/camera/om/dmc-fz300_en_adv_om.pdf
. Page 78 covers the Handheld Night Shot and page 126 covers the HDR mode. Look in the box with the blue background for these limits.
I hope this helps.