Copy/paste images from phone to desktop, files are corrupted and huge (2gb+)

I linked my Android phone (v6.0) to my Windows laptop, located the phone's DCIM folder in File Manager and copy/pasted images from my phone onto my laptop's hard drive. Some of the images are corrupted, can't be recognised as a bitmap, and are 2GB+ whereas on the phone they would have been 2-5MB. It seems to be a date thing, as it is all images past a certain date. It also affected some videos and again it is all videos past a certain date, although a different date to the images. Is this a common problem, and what causes it? I'm assuming the images are lost as I deleted them from the phone once I saw they had successfully been pasted, without checking that the files were still readable.