Partitions have vanished!

[PsypherPunk]

i woke up this morning to find that all the logical partitions on my second hard drive have vanished! fdisk -l for this drive now turns up:

Disk /dev/hdb: 163.9 GB, 163928604672 bytes
255 heads, 63 sectors/track, 19929 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/hdb1               1        2611    20972826   93  Amoeba
/dev/hdb2            2612        7833    41945715   93  Amoeba
/dev/hdb3            7834       19928    97153087+  1f  Unknown
/dev/hdb4           19929       19929        8032+   e  W95 FAT16 (LBA)

However, prior to shutting down last night hdb4 didn't exist and hdb3 was an extended partition containing hdb5-9 (and several distros!). Thankfully there was nothing particularly important on any of the partitions but what's happened!?

Is there any way to recover the data?

[PsypherPunk]

i've just spotted something - hdb3 (which was supposed to be an Extended partition in which the other Logical partitions existed) is showing as type '1f' whereas it should be type '5', shouldn't it?

If anyone could confirm this, that'd be great. Or suggest any way to change the type without formatting.