Ubuntu – Partition wiped after distribution update

My problem: a partition and its files disappeared unbeknownst to me, most likely after updating from 12.10 to 13.04 (though not sure).

Before Ubuntu 12.10 I was running Windows 7, with a hard drive of 250 GB partitioned in two: drive C and drive D. The former for system files, the latter for personal files. I formatted the C drive and installed Ubuntu 12.10 onto it from a Live CD. Afterwards, drive D and its files were available under an icon in the launcher, similar to the one that appears after connecting a USB stick or an external hard drive. The drive was also available through a folder in home\media.

The first moment I noticed it gone was after the update to Ubuntu 13.04. It's gone. I have done nothing I can think of to trigger it. I ran multiple searches on the entire filesystem querying filenames I surefire knew were on that partition, with no result.

Anyone can help?

EDIT 1: release upgrade was done via the default software updater from within Ubuntu 12.10

EDIT 2: Output from sudo fdisk -l via terminal:

> Disk /dev/sda: 250.1 GB, 250059350016 bytes 255 heads, 63
> sectors/track, 30401 cylinders, total 488397168 sectors Units =
> sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512
> bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes
> Disk identifier: 0x000a1062
> 
>    Device Boot      Start         End      Blocks   Id  System
> /dev/sda1   *        2048      499711      248832   83  Linux
> /dev/sda2          501758   488396799   243947521    5  Extended
> /dev/sda5          501760   488396799   243947520   8e  Linux LVM
> 
> Disk /dev/mapper/ubuntu-root: 247.7 GB, 247661068288 bytes 255 heads,
> 63 sectors/track, 30109 cylinders, total 483713024 sectors Units =
> sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512
> bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes
> Disk identifier: 0x00000000
> 
> Disk /dev/mapper/ubuntu-root doesn't contain a valid partition table
> 
> Disk /dev/mapper/ubuntu-swap_1: 2134 MB, 2134900736 bytes 255 heads,
> 63 sectors/track, 259 cylinders, total 4169728 sectors Units = sectors
> of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512
> bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk
> identifier: 0x00000000

EDIT 3: output from sudo blkid via terminal:

> /dev/sda1: UUID="a41e3612-9597-43cc-87c8-9234ff3eeece" TYPE="ext2" 
> /dev/sda5: UUID="XPdn1E-G8g0-zhet-DDuI-QfCf-7d2T-5pQqUx" TYPE="LVM2_member"
> /dev/mapper/ubuntu-root: UUID="8015cbb9-38ed-4a82-8b92-67c80a2ab1eb" TYPE="ext4" 
> /dev/mapper/ubuntu-swap_1: UUID="5d5096ba-623b-4da0-b133-429388b606df" TYPE="swap"