Basically what the subject says. I have heard Wormphlegm. So don't recommend that Thanks

Catacombs, of Darkness, Senthil, and Funeralium should suffice.

All of those are really dark and extreme, and some like Wormphelgm are more in the vein of the torture sound.

I don't think it can be terrifying AND sucidal; it's two different moods imo.
Tyranny could be seen as playing some 'terrifying' funeral doom
While Yhdarl would be kind of 'suicidal' ?? (man, is that tag ridiculous!)
I'd say Of Darkness is neither terrifying nor suicidal, just terribly oppressive.

Might I suggest Comatose Vigil?

i would say Elysian Blaze's new album blood geometry

Planet AIDS - ''Apokalyptik AIDS''. It's not really suicidal, but it's really dark and scary, and check out Mordor too.

Second this, I recommend checking out their earlier work as well.

I also suggest giving fellow countrymen Abyssmal Sorrow and Funeral Mourning a listen, as well as Loss' Despond. Not overall terrifying, but definitely some depressing, emotionally draining music.

It's not so much terrifying as it is desolate, but Nortt might just be suicidal enough for you.

Oh My! I wasn't aware of that new release. I'm listening to it right now, this is massive! Their best so far, absolutely no doubt about it. I kind of had let that band down, but what a mistake! It's very strong!

http://www.youtube.com/watch?v=_C6nzLzwYyc\
Black Crow King, definitely one of my favorite Funeral Doom acts.

*cracks knuckles*

If you like Wormphlegm, I'll have to go ahead and second Of Darkness, Catacombs, Tyranny and Funeralium. However, the style they all play isn't so much terrifying as it is desolate. Tyranny can get under your skin if you are in the right mood.

But so can Murkrat, just the vocals are so haunting and eerie... excellent funeral doom!

Despite its depressive nature, funeral doom isn't quite as suicidal as DSBM (Depressive/Suicidal black metal, where a majority of bands have lyrics about suicide and death). Terrifying can be subjective as well - Tyranny's Bleak Vistae is a creepy sounding album, it has those haunting guitar leads that can intrigue you but... it evokes images of monsters hiding in the dark as you sleep ready to crawl out and slither their tentacles into your ear invoking such a horrible nosebleed that most of your blood volume is spilling out of your nostrils, down your face and into your throat causing a simultaneous incidence of exsanguination and drowning in your own blood, awakening you from a nightmare only to enter in a far more horrific nightmare just before you are sent to wherever the fuck we go when we die. However, on some nights I listen to Tyranny to relax, and it can be quite relaxing and pleasing.

Longing for Dawn has been one of my favorites of the desolate hybrid of ambient and funeral doom, if you like the style of Comatose Vigil I think you'll enjoy Longing for Dawn. Comatose Vigil is a bit slower and more desolate, while Longing for Dawn is quite "busy" with ambient soundscapes among their music.

Mournful Congregation is one of my favorite bands period, with six masterpieces on their belt (two demos, plus four full length albums). They have a song called Suicide Choir that you might enjoy. However, this style of funeral doom is more melodic and busy than the previous bands I've mentioned (although Murkrat is fairly busy as well).

Along a similar line of melodic funeral doom is a band called Worship. They've released several splits with various bands of the style and are quite, well, worshipped, among funeral doom bands.

The Norwegian band Funeral is one of the oldest funeral doom bands, only a handful of others (Mordor, Voj, Thergothon, Skepticism) have been around longer. Only their first two albums are funeral doom, afterward they moved toward a faster paced doom/death sound, with recent albums having mostly clean singing.

Mordor was mentioned before, but I ought to touch on this band. This is very strange and unsettling stuff.

Voj might be up your alley as well. Voj is a Russian band that developed its own funeral doom sound independent of Thergothon's. Both of their releases precede Thergothon, one of them being a demo from 1989 (I would love to get my hands on this!).

Bosque produces some fairly creepy funeral doom. They did a split with Senthil with their half being called "Under the Capricorn Sky". Some excellent if unsettling stuff!

Bethlehem's 1st two albums should do the trick for you. They have a good mix of terrifying, suicidal, and insane moments.
http://www.youtube.com/watch?v=ncO9lXdsD_Y