Can african dwarf frogs get depressed?

Quick little explanation:

I was given a pair of african dwarf frogs (bought from Green Earth store) about 4 years ago and unfortunately had to bury one the other day. The remaining froggy however has become very lethargic in behaviour...

1. Species- African Dwarf Frog, (male?). Issue- Depressed/grieving. Reasoning- Drastic change in behaviour. He had become a much more active swimmer since getting a bigger tank and doing his freeze-frame poses often. Since the death of the other frog he has not been swimming around. Spent first day alone in hidey-cave for whole day. Spent today slowly crawling along bottom of tank. Though hiding is still a normal ADf behaviour I know, its the way he just has been slowly drifting around the bottom and never coming off the gravel.

2. I'm sorry, I don't have this information. Since I got them I have always used Fiji brand water to fill tank during water changes.

3. Size- 2.5 gallon/10L with lid. Set Up- New tank was set up on January 30, 2016.

4. Filter- TOM Mini Internal Filter. Item #1250 Details- 1-5gallon aquariums. 3stage filtration (mechanical, chemical, biological). Foam cartridge and carbon. Spray bar and adjustable water flow (set to lowest speed= 45 gallons/hour). Low voltage = AC 12V. Filter is only turned on for about 1-3 hours each day as not to stress frogs. Heater- Aqueon mini heater. 10w, 120v.

5. There is only 1 small african dwarf frog now. Approximately 3/4" body length (Not including arms and legs). Slim body but not too skinny.

6. I have had the pair for about 4 years. (One died only yesterday- Found him in the morning with a bloated stomach stuck floating on the surface. Was not able to swim to bottom. Would barrel role when lost control trying to swim. Found him a few hours later after work on the tank floor dead.) Acclimation- added them to the new tank set up, then turned heater on for first time to warm up water with them in it. Filter and heater were new additions to the bigger tank which is new as well. (Jan. 30). Both frogs were doing very well in new set up until yesterday.

7. Anything that was new was added the first week (at most) when they new tank was set up. The only other thing was I started adding freeze-dried blood worms every couple days to their meal times of the aquatic frog micro pellets. (After some research on the internet I'm starting to think that the blood worms, freeze-dried, frozen, or fresh, are not as beneficial as I was originally lead to believe.) I believe the blood worms may be the cause of death to my poor frog but it can't be confirmed.